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1. and get SNO SNAME COUNT eee sE EG EC 1 Smith 2 3 Adams 2 4 Blake 3 Subqueries In the WHERE and HAVING clauses the use of subqueries subselects is allowed in every place where a value is expected In this case the value must be derived by evaluating the subquery first The usage of subqueries extends the expressive power of SQL Example 2 8 Subselect If we want to know all parts having a greater price than the part named Screw we use the query 18 Chapter 2 SOL SELECT FROM PART WHERE PRICE gt SELECT PRICE FROM PART WHERE PNAME Screw The result is PNO PNAME PRICE A e ETE A 3 Bolt 15 4 Cam 25 When we look at the above query we can see the keyword SELECT two times The first one at the beginning of the query we will refer to it as outer SELECT and the one in the WHERE clause which begins a nested query we will refer to it as inner SELECT For every tuple of the outer SELECT the inner SELECT has to be evaluated After every evaluation we know the price of the tuple named Screw and we can check if the price of the actual tuple is greater If we want to know all suppliers that do not sell any part e g to be able to remove these suppliers from the database we use SELECT FROM SUPPLIER S WHERE NOT EXISTS SELECT FROM SELLS SE WHERE SE SNO S SNO In our example the result will be empty because every supplier sells at least one part Note that we use S SNO fro
2. UPDATE weather SET temp hi temp hi 2 temp_lo temp lo 2 WHERE date gt 11 28 1994 Deletions Deletions are performed using the delete command DELETE FROM weather WHERE city Hayward All weather recording belongs to Hayward is removed One should be wary of queries of the form DELETE FROM classname Without a qualification delete will simply remove all instances of the given class leaving it empty The system will not request confirmation before doing this Using Aggregate Functions Like most other query languages PostgreSQL supports aggregate functions The current implementation of Postgres aggregate functions have some limitations Specifically while there are aggregates to compute such functions as the count sum avg average max maximum and min minimum over a set of instances aggregates can only appear in the target list of a query and not directly in the qualification the where clause As an example SELECT max temp_lo FROM weather 1s allowed while SELECT city FROM weather WHERE temp _lo max temp_lo 1s not However as is often the case the query can be restated to accomplish the intended result here by using a subselect SELECT city FROM weather WHERE temp _lo SELECT max temp_lo FROM weather 36 Chapter 5 The Query Language Aggregates may also have group by clauses SELECT city max temp_lo FROM weather GROUP BY city 37 Chapter 6 Advanced Postgres SQL
3. low high city low high San Francisco 43 57 San Francisco 46 50 San Francisco 37 54 San Francisco 46 50 Note The semantics of such a join are that the qualification is a truth expression defined for the Cartesian product of the classes indicated in the query For those instances in the Cartesian product for which the qualification is true Postgres computes and returns the values specified in the target list Postgres SQL does not assign any meaning to duplicate values in such expressions This means that Postgres sometimes recomputes the same target list several times this frequently happens when Boolean expressions are connected with an or To remove such duplicates you must use the select distinct statement In this case both W1 and W2 are surrogates for an instance of the class weather and both range over all instances of the class In the terminology of most database systems W1 and W2 are known as range variables A query can contain an arbitrary number of class names and surrogates 35 Chapter 5 The Query Language Updates You can update existing instances using the update command Suppose you discover the temperature readings are all off by 2 degrees as of Nov 28 you may update the data as follow
4. 1987 this ANSI standard was also accepted as an international standard by the International Organization for Standardization ISO This original standard version of SQL is often referred to informally as SQL 86 In 1989 the original standard was extended and this new standard is often again informally referred to as SQL 89 Also in 1989 a related standard called Database Language Embedded SQL ESQL was developed The ISO and ANSI committees have been working for many years on the definition of a greatly expanded version of the original standard referred to informally as SQL2 or SQL 92 This version became a ratified standard International Standard ISO IEC 9075 1992 Database Language SQL in late 1992 SQL 92 is the version normally meant when people refer to the SQL standard A detailed description of SQL 92 is given in Date and Darwen 1997 At the time of writing this document a new standard informally referred to as SQL3 is under development It is planned to make SQL a Turing complete language i e all computable queries e g recursive queries will be possible This is a very complex task and therefore the completion of the new standard can not be expected before 1999 The Relational Data Model As mentioned before SQL is a relational language That means it is based on the relational data model first published by E F Codd in 1970 We will give a formal description of the relational model later in Relational Data Model Form
5. Para e pesa as e ponposa Mariposa 1320 1953 patena ans PRA pon 40 Chapter 6 Advanced Postgres SOL Features Postgres will automatically find the version of Mariposa s record valid at the current time One can also give a time range For example to see the past and present populations of Mariposa one would query SELECT name population FROM cities epoch now WHERE name Mariposa where epoch indicates the beginning of the system clock Note On UNIX systems this is always midnight January 1 1970 GMT If you have executed all of the examples so far then the above query returns name population Mariposa 1200 Mariposa 1320 P The default beginning of a time range is the earliest time representable by the system and the default end is the current time thus the above time range can be abbreviated as More Advanced Features Postgres has many features not touched upon in this tutorial introduction which has been oriented toward newer users of SQL These are discussed in more detail in both the User s and Programmer s Guides 41 Bibliography Selected references and readings for SQL and Postgres SQL Reference Books The Practical SQL Handbook Using Structured Query Language 3 Judity Bowman Sandra Emerson and Marcy Damovsky 0 201 44787 8 1996 Ad
6. R To create an index in SQL the CREATE INDEX command is used The syntax is CREATE INDEX index name ON table name name of attribute Example 2 11 Create Index To create an index named I on attribute SNAME of relation SUPPLIER we use the following statement CREATE INDEX 1 ON SUPPLIER SNAME The created index is maintained automatically i e whenever a new tuple is inserted into the relation SUPPLIER the index I is adapted Note that the only changes a user can percept when an index is present are an increased speed 21 Chapter 2 SOL Create View A view may be regarded as a virtual table 1 e a table that does not physically exist in the database but looks to the user as if it does By contrast when we talk of a base table there is really a physically stored counterpart of each row of the table somewhere in the physical storage Views do not have their own physically separate distinguishable stored data Instead the system stores the definition of the view i e the rules about how to access physically stored base tables in order to materialize the view somewhere in the system catalogs see System Catalogs For a discussion on different techniques to implement views refer to SIM98 In SQL the CREATE VIEW command is used to define a view The syntax is CREATE VIEW view_name AS select_stmt where select_stmt is a valid select statement as defined in Select Note that select_stmt is not executed when the
7. capability In SQL it is possible to involve arithmetic operations as well as comparisons e g A lt B 3 Note that or other arithmetic operators appear neither in relational algebra nor in relational calculus Assignment and Print Commands It is possible to print a relation constructed by a query and to assign a computed relation to a relation name Aggregate Functions Operations such as average sum max etc can be applied to columns of a relation to obtain a single quantity Select The most often used command in SQL is the SELECT statement used to retrieve data The syntax is SELECT ALLIDISTINCT lexpr_1 AS c_alias_1 expr_k AS c_alias_k FROM table_name_1 t_alias_1 L table_name_n t_alias_n WHERE condition GROUP BY name_of_attr_i L name_of_attr_j HAVING condition UNION ALL INTERSECT EXCEPT SELECT ORDER BY name_of_attr_i ASCIDESC name_of_attr_j ASCIDESC Now we will illustrate the complex syntax of the SELECT statement with various examples The tables used for the examples are defined in The Suppliers and Parts Database Simple Selects Here are some simple examples using a SELECT statement Example 2 4 Simple Query with Qualification To retrieve all tuples from table PART where the attribute PRICE is greater than 10 we formulate the following query SELECT FROM PART WHERE PRICE gt 10 14 Chapter 2 SOL and get the tab
8. database postgres failed connectDB failed Is the postmaster running and accepting TCP IP with i connections at localhost on port 5432 1t is usually because 1 the postmaster is not running or 2 you are attempting to connect to the wrong server host If you get the following error message FATAL 1 Feb 17 23 19 55 process userid 2360 database owner 268 1t means that the site administrator started the postmaster as the wrong user Tell him to restart it as the Postgres superuser Managing a Database Now that Postgres is up and running we can create some databases to experiment with Here we describe the basic commands for managing a database Most Postgres applications assume that the database name if not specified is the same as the name on your computer account If your database administrator has set up your account without database creation privileges then she should have told you what the name of your database is If this is the case then you can skip the sections on creating and destroying databases Creating a Database Let s say you want to create a database named mydb You can do this with the following command 29 Chapter 4 Getting Started createdb mydb If you do not have the privileges required to create a database you will see the following createdb mydb WARN user your username is not allowed to create destroy databases createdb database creation failed on mydb Po
9. ho 1 2 3 3 a b 1 2 3 6 c d 4 5 6 3 a b 4 5 6 6 e d 7 8 9 3 a b T 8 9 6 Cc d After the selection R C S C R x S we get A B RC sS c D E E pees as Pres a ai 11 Chapter 2 SOL AB Ob OVW OVW To remove the duplicate column S C we project it out by the following operation OR A R B R C S D S E 6R C S C R x S and get A B c D E a e Sas ae 1 2 3 a b 4 5 6 cj a DIVIDE Let R be a table with the attributes A B C and D and let S be a table with the attributes C and D Then we define the division as R S t V ts e S 3 tr e R such that tr A B txtr C D ts where tr x y denotes a tuple of table R that consists only of the components x and y Note that the tuple t only consists of the components A and B of relation R Given the following tables R A B C D s Cc D o a S o tSS3 a b E d c d a b e f e f b c e f e d c d e d e a b d e R S is derived as For a more detailed description and definition of the relational algebra refer to Ullman 1988 or Date 1994 Example 2 3 A Query Using Relational Algebra Recall that we formulated all those relational operators to be able to retrieve data from the database Let s return to our example from the previous section Operations in the Relational Data Model where someone wanted to know the names of all suppliers that sell the part Screw This question can be answered using relational algebra by the following o
10. the database and cannot be undone so this should only be done with a great deal of forethought 31 Chapter 5 The Query Language The Postgres query language is a variant of the SQL3 draft next generation standard It has many extensions such as an extensible type system inheritance functions and production rules These are features carried over from the original Postgres query language PostQuel This section provides an overview of how to use Postgres SQL to perform simple operations This manual is only intended to give you an idea of our flavor of SQL and is in no way a complete tutorial on SQL Numerous books have been written on SQL including MELT93 and DATE97 You should be aware that some language features are extensions to the ANSI standard Interactive Monitor In the examples that follow we assume that you have created the mydb database as described in the previous subsection and have started psql Examples in this manual can also be found in lasr local pgsql src tutorial Refer to the README file in that directory for how to use them To start the tutorial do the following cd usr local pgsql src tutorial psql s mydb Welcome to the POSTGRESQL interactive sql monitor Please read the file COPYRIGHT for copyright terms of POSTGRESQL type for help on slash commands type q to quit type g or terminate with semicolon to execute query You are currently connected to the database postgres mydb gt i basics
11. the shared buffer pool and lock table associated with a postmaster site therefore this is not recommended in a multiuser site Notation or usr local pgsq at the front of a file name is used to represent the path to the Postgres superuser s home directory Chapter 1 Introduction In a command synopsis brackets and indicate an optional phrase or keyword Anything in braces and and containing vertical bars indicates that you must choose one In examples parentheses and are used to group boolean expressions is the boolean operator OR Examples will show commands executed from various accounts and programs Commands executed from the root account will be preceeded with gt Commands executed from the Postgres superuser account will be preceeded with while commands executed from an unprivileged user s account will be preceeded with SQL commands will be preceeded with gt or will have no leading prompt depending on the context Note At the time of writing Postgres v6 5 the notation for flagging commands is not universally consistant throughout the documentation set Please report problems to the Documentation Mailing List mailto docs postgresql org Y2K Statement Author Written by Thomas Lockhart mailto lockhart alumni caltech edu on 1998 10 22 The PostgreSQL Global Development Team provides the Postgres software code tree as a public service without warranty and without liabi
12. type can be created To illustrate their use we first create a class with arrays of base types CREATE TABLE SAL EMP name text pay by quarter int4 schedule text 1 1 i The above query will create a class named SAL_EMP with a text string name a one dimensional array of int4 pay_by_quarter which represents the employee s salary by quarter and a two dimensional array of text schedule which represents the employee s weekly schedule Now we do some INSERTSs note that when appending to an array we enclose the values within braces and separate them by commas If you know C this is not unlike the syntax for initializing structures INSERT INTO SAL EMP VALUES Bill See 10000 10000 1 0000 meeting lunch 00 DS INSERT INTO SAL EMP VALUES Carol can 25000 25000 25000 talk consult meeting By default Postgres uses the one based numbering convention for arrays that is an array of n elements starts with array 1 and ends with array n Now we can run some queries on SAL_EMP First we show how to access a single element of an array at a time This query retrieves the names of the employees whose pay changed in the second quarter 39 Chapter 6 Advanced Postgres SOL Features SELECT name FROM SAL EMP WHERE SAL EMP pay by quarter 1 lt gt SAL EMP pay by quarter 2 name Carol This query retrieves the thir
13. 987 M Stonebraker E Hanson and C H Hong Feb 1987 Conference on Data Engineering Los Angeles CA IEEE 1987 The Postgres Storage System Stonebraker 1987 M Stonebraker Sept 1987 VLDB Conference Brighton England 1987 A Commentary on the Postgres Rules System Stonebraker et al 1989 M Stonebraker M Hearst and S Potamianos Sept 1989 Record 18 3 SIGMOD 1989 The case for partial indexes DBMS http s2k ftp CS Berkeley EDU 8000 postgres papers ERL M89 17 pdf Stonebraker M 1989b M Stonebraker Dec 1989 Record 18 no 4 4 11 SIGMOD 1989 The Implementation of Postgres Stonebraker Rowe Hirohama 1990 M Stonebraker L A Rowe and M Hirohama March 1990 Transactions on Knowledge and Data Engineering 2 1 IEEE On Rules Procedures Caching and Views in Database Systems Stonebraker et al ACM 1990 M Stonebraker and et al June 1990 Conference on Management of Data ACM SIGMOD 43
14. Features Having covered the basics of using Postgres SQL to access your data we will now discuss those features of Postgres that distinguish it from conventional data managers These features include inheritance time travel and non atomic data values array and set valued attributes Examples in this section can also be found in advance sql in the tutorial directory Refer to Chapter 5 for how to use it Inheritance Let s create two classes The capitals class contains state capitals which are also cities Naturally the capitals class should inherit from cities CREATE TABLE cities name text population float altitude int in ft i CREATE TABLE capitals state char2 INHERITS cities In this case an instance of capitals inherits all attributes name population and altitude from its parent cities The type of the attribute name is text a native Postgres type for variable length ASCII strings The type of the attribute population is float a native Postgres type for double precision floating point numbers State capitals have an extra attribute state that shows their state In Postgres a class can inherit from zero or more other classes and a query can reference either all instances of a class or all instances of a class plus all of its descendants Note The inheritance hierarchy is a directed acyclic graph For example the following query finds all the cities that are situated at an attitude of 500ft or
15. Non Atomnic Valsson iei e A A E A iE 39 DT Sia rd 39 O O AAN 40 More Advanced Peatures cscccsicessesssisessscseessvsecccertuvsaacenc E ea Ei i E Eia e 41 Bibliography sscocssisicccsssvnensesescsecssonssesssonessaseaseapseesscapdessessceosseesseonsn eneo rosno oin osr asiaa 42 11 List of Figures 3 1 How a connection is established 111 List of Examples 2 1 The Suppliers and Parts Database sinoni a e eiee ESK EE EE 9 22AN mner Jnae ER E EEE E AE A E A E E e 11 2 3 A Query Using Relational Algebra ooonnnnninnnonnnonnonoconoconcconcnnoconocnnonononncon arco nono nonnconncnnnenns 12 2 4 Simple Query with Qualification oooonnnconnnocnnonconnconoconcnnnconoco nono non nooo nono no rn nora con nc rn nora ncnn ninos 14 2 5 ABOT DALOS iis ssszcdisessscsenss Sbssessasscavsctbdecyatessvegusadssbeassapeisdssast sa sheedsadsvenstendeedsdessesss ciclistas 16 2 62 AB ON 17 ZA VIO a ia 18 A O bees ERESSE ST 18 2 9 Union Intersect Except o ches 19 2 10 Table Creation A pd 20 D221 1 Create A RN 21 iv Summary Postgres developed originally in the UC Berkeley Computer Science Department pioneered many of the object relational concepts now becoming available in some commercial databases It provides SQL92 SQL3 language support transaction integrity and type extensibility PostgreSQL is a public domain open source descendant of this original Berkeley code Chapter 1 Introduction What This document is the user m
16. PostgreSQL Tutorial The PostgreSQL Development Team Edited by Thomas Lockhart PostgreSQL Tutorial by The PostgreSQL Development Team Edited by Thomas Lockhart PostgreSQL is Copyright O 1996 9 by the Postgres Global Development Group Table of Contents SUMIMALY AO A E O A E O E O E O O A T i 1 Introduction i AEE E E E A E 1 W hatis Post tot dd a a ae Na 1 A Short History of Postgres c ssessssscsssseseivasupescse del sstestesseas EREE EEEE EEE EErEE 2 The Berkeley Postgres Project cceesceceseesceceseceeeeceeeeeencecueecsaeceeeeecaeceeneecsaecenees 2 Postres it na 2 Posteres Ol inicia aa 3 About This Release viii e id Es eee 3 RGSOUICES iii ASA dit 4 SS epeasssesstvt sueacueasved shea ae epsessacap dest EEE EASE SES EEEE Ea Ei 5 NOfatlon site Bios dais 5 V2K Statement acs seiiiis eases Mase det 6 Copyrights and Trademarks ivis eese teense isos tina 6 De SOL A ANNAN 8 The Relational Data Model 000 eee ceeecseeeseeeeecaeecseeeeeseeeeseeeeeeeeeesecsecsaecaecsaessaeeaeeeas 8 Relational Data Model Formalities oooooccconnnoninoncnnnnonnnononancnnncnnnc nono no cn nooo nooo no rncon nono nonnnenns 9 Domains vs Data Types escisiones tesina haus bessactsbsteoesbasselubes EE E 10 Operations in the Relational Data Model oonncnnncnncniccnocnnonconoconoconcconcn noc no cono rn nono nonncnnnonns 10 Relational Al Se Bray eree rre ponen details des EEOAE aessbesseoeay ou evessh vader seedmore 24s 10 Relational Calculus
17. Release PostgreSQL is available without cost This manual describes version 6 5 of PostgreSQL We will use Postgres to mean the version distributed as PostgreSQL Check the Administrator s Guide for a list of currently supported machines In general Postgres is portable to any Unix Posix compatible system with full libc library support Chapter 1 Introduction Resources This manual set is organized into several parts Tutorial An introduction for new users Does not cover advanced features User s Guide General information for users including available commands and data types Programmer s Guide Advanced information for application programmers Topics include type and function extensibility library interfaces and application design issues Administrator s Guide Installation and management information List of supported machines Developer s Guide Information for Postgres developers This is intended for those who are contributing to the Postgres project application development information should appear in the Programmer s Guide Currently included in the Programmer s Guide Reference Manual Detailed reference information on command syntax Currently included in the User s Guide In addition to this manual set there are other resources to help you with Postgres installation and use man pages The man pages have general information on command syntax FAQs The Frequently Asked Questions FAQ doc
18. SELECT Queries Any select query can be redirected to a new class SELECT INTO TABLE temp FROM weather 34 Chapter 5 The Query Language This forms an implicit create command creating a new class temp with the attribute names and types specified in the target list of the select into command We can then of course perform any operations on the resulting class that we can perform on other classes Joins Between Classes Thus far our queries have only accessed one class at a time Queries can access multiple classes at once or access the same class in such a way that multiple instances of the class are being processed at the same time A query that accesses multiple instances of the same or different classes at one time is called a join query As an example say we wish to find all the records that are in the temperature range of other records In effect we need to compare the temp_lo and temp_hi attributes of each EMP instance to the temp_lo and temp_hi attributes of all other EMP instances Note This is only a conceptual model The actual join may be performed in a more efficient manner but this is invisible to the user We can do this with the following query SELECT Wl city Wl temp lo AS low Wl temp hi AS high W2 city W2 temp_lo AS low W2 temp hi AS high FROM weather W1 weather W2 WHERE W1 temp_ lo lt W2 temp_lo AND W1 temp hi gt W2 temp_ hi city
19. alities but first we want to have a look at it from a more intuitive point of view Chapter 2 SOL A relational database is a database that is perceived by its users as a collection of tables and nothing else but tables A table consists of rows and columns where each row represents a record and each column represents an attribute of the records contained in the table The Suppliers and Parts Database shows an example of a database consisting of three tables SUPPLIER is a table storing the number SNO the name SNAME and the city CITY of a supplier PART is a table storing the number PNO the name PNAME and the price PRICE of a part SELLS stores information about which part PNO is sold by which supplier SNO It serves in a sense to connect the other two tables together Example 2 1 The Suppliers and Parts Database SUPPLIER SNO SNAME CITY SELLS SNO PNO 1 Smith London sl 1 2 Jones Paris 1 2 3 Adams Vienna 2 4 4 Blake Rome 3 1 3 3 4 2 PART PNO PNAME PRICE 4 3 eae Pi y o Te ld 4 4 1 Screw 10 2 Nut 8 3 Bolt 15 4 Cam 25 The tables PART and SUPPLIER may be regarded as entities and SELLS may be regarded as a relationship between a particular part and a particular supplier As we will see later SQL operates on tables like the ones just defined but before that we will study the theory of the relational model Relational Data Model Formalities The mathematical conce
20. anual for the PostgreSQL http postgresql org database management system originally developed at the University of California at Berkeley PostgreSQL is based on Postgres release 4 2 http s2k ftp CS Berkeley EDU 8000 postgres postgres html The Postgres project led by Professor Michael Stonebraker was sponsored by the Defense Advanced Research Projects Agency DARPA the Army Research Office ARO the National Science Foundation NSF and ESL Inc is Postgres Traditional relational database management systems DBMSs support a data model consisting of a collection of named relations containing attributes of a specific type In current commercial systems possible types include floating point numbers integers character strings money and dates It is commonly recognized that this model is inadequate for future data processing applications The relational model successfully replaced previous models in part because of its Spartan simplicity However as mentioned this simplicity often makes the implementation of certain applications very difficult Postgres offers substantial additional power by incorporating the following four additional basic concepts in such a way that users can easily extend the system classes inheritance types functions Other features provide additional power and flexibility constraints triggers rules transaction integrity These features put Postgres into the category of databases referred
21. cates that the terminal monitor is listening to you and that you can type SQL queries into a workspace maintained by the terminal monitor The psql program responds to escape codes that begin with the backslash character For example you can get help on the syntax of various Postgres SQL commands by typing mydb gt h Once you have finished entering your queries into the workspace you can pass the contents of the workspace to the Postgres server by typing mydb gt g This tells the server to process the query If you terminate your query with a semicolon the g is not necessary psql will automatically process semicolon terminated queries To read queries from a file say myFile instead of entering them interactively type 30 Chapter 4 Getting Started mydb gt i fileName To get out of psql and return to UNIX type mydb gt q and psql will quit and return you to your command shell For more escape codes type h at the monitor prompt White space 1 e spaces tabs and newlines may be used freely in SQL queries Single line comments are denoted by Everything after the dashes up to the end of the line is ignored Multiple line comments and comments within a line are denoted by Destroying a Database If you are the database administrator for the database mydb you can destroy it using the following UNIX command destroydb mydb This action physically removes all of the UNIX files associated with
22. client server application As a user you only need access to the client portions of the installation an example of a client application is the interactive monitor psql For simplicity we will assume that Postgres has been installed in the directory usr local pgsql Therefore wherever you see the directory usr local pgsql you should substitute the name of the directory where Postgres is actually installed All Postgres commands are installed in the directory usr local pgsql bin Therefore you should add this directory to your shell command path If you use a variant of the Berkeley C shell such as csh or tcsh you would add set path usr local pgsql bin path in the login file in your home directory If you use a variant of the Bourne shell such as sh ksh or bash then you would add PATH usr local pgsql bin PATH export PATH o o to the profile file in your home directory From now on we will assume that you have added the Postgres bin directory to your path In addition we will make frequent reference to setting a shell variable or setting an environment variable throughout this document If you did not fully understand the last paragraph on modifying your search path you should consult the UNIX manual pages that describe your shell before going any further If your site administrator has not set things up in the default way you may have some more work to do For example if the database server machine is a rem
23. d quarter pay of all employees SELECT SAL EMP pay by quarter 3 FROM SAL EMP A AAA AAA pay_by quarter Hiei Rie Brie e 10000 A e a 25000 Pa AAA SS We can also access arbitrary slices of an array or subarrays This query retrieves the first item on Bill s schedule for the first two days of the week SELECT SAL EMP schedule 1 2 1 1 FROM SAL EMP WHERE SAL EMP name P Bid Ly schedule A A NP a ee i meeting Time Travel As of Postgres v6 2 time travel is no longer supported There are several reasons for this performance impact storage size and a pg_time file which grows toward infinite size in a short period of time New features such as triggers allow one to mimic the behavior of time travel when desired without incurring the overhead when it is not needed for most users this is most of the time See examples in the contrib directory for more information Time travel is deprecated The remaining text in this section is retained only until it can be rewritten in the context of new techniques to accomplish the same purpose Volunteers thomas 1998 01 12 Postgres supports the notion of time travel This feature allows a user to run historical queries For example to find the current population of Mariposa city one would query SELECT FROM cities WHERE name Mariposa 4 PE soos name population altitude
24. dison Wesley 1997 A Guide to the SQL Standard A user s guide to the standard database language SQL 4 C J Date and Hugh Darwen 0 201 96426 0 1997 Addison Wesley 1997 An Introduction to Database Systems 6 C J Date 1 1994 Addison Wesley 1994 Understanding the New SQL A complete guide Jim Melton and Alan R Simon 1 55860 245 3 1993 Morgan Kaufmann 1993 Abstract Accessible reference for SQL features Principles of Database and Knowledge Base Systems Jeffrey D Ullman 1 Computer Science Press 1988 PostgreSQL Specific Documentation The PostgreSQL Administrator s Guide The Administrator s Guide Edited by Thomas Lockhart 1998 10 01 The PostgreSQL Global Development Group The PostgreSQL Developer s Guide The Developer s Guide Edited by Thomas Lockhart 1998 10 01 The PostgreSQL Global Development Group The PostgreSQL Programmer s Guide The Programmer s Guide Edited by Thomas Lockhart 1998 10 01 The PostgreSQL Global Development Group The PostgreSQL Tutorial Introduction The Tutorial Edited by Thomas Lockhart 1998 10 01 The PostgreSQL Global Development Group The PostgreSQL User s Guide The User s Guide Edited by Thomas Lockhart 1998 10 01 The PostgreSQL Global Development Group Enhancement of the ANSI SQL Implementation of PostgreSQL Simkovics 1998 Stefan Simkovics O Univ Prof Dr Georg Gottlob November 29 1998 Department of Information Syst
25. do this The statement is divided into a target list the part that 33 Chapter 5 The Query Language lists the attributes to be returned and a qualification the part that specifies any restrictions For example to retrieve all the rows of weather type SELECT FROM WEATHER and the output should be ii eopet A ni hret mes alee HERAS ee epi eet er city temp_lo temp_hi prep date PA A Oe ARS o E A ede ase PA San Francisco 46 50 0 25 11 27 1994 PRS Ae a ee ti Pata eee es As da PS A ta at San Francisco 43 57 o 11 29 1994 a E E PR ie a PA ee Fesas Sere Re Ses Hayward 37 54 11 29 1994 SR SAA AA HA ts pase na Ea E Sea ee ee You may specify any arbitrary expressions in the target list For example you can do SELECT city temp _hi temp_lo 2 AS temp_avg date FROM weather Arbitrary Boolean operators and or and not are allowed in the qualification of any query For example SELECT FROM weather WHERE city San Francisco AND prcp gt 0 0 results in ASS A E PS q a SSS Ho Pp city temp_lo temp hi prcp date IS Seo SS Poca SSS a 0 prasata PE San Francisco 46 50 0 25 11 27 1994 ii eta mi cia eS oS RS ts gt Po SST sete As a final note you can specify that the results of a select can be returned in a sorted order or with duplicate instances removed SELECT DISTINCT city FROM weather ORDER BY city Redirecting
26. e The most fundamental command for data definition is the one that creates a new relation a new table The syntax of the CREATE TABLE command is CREATE TABLE table name name of attr_1 type of attr 1 name of attr 2 type of attr 2 lo l Example 2 10 Table Creation To create the tables defined in The Suppliers and Parts Database the following SQL statements are used CREATE TABLE SUPPLIER SNO INTEGER SNAME VARCHAR 20 CITY VARCHAR 20 CREATE TABLE PART PNO INTEGER 20 Chapter 2 SOL PNAME VARCHAR 20 PRICE DECIMAL 4 2 CREATE TABLE SELLS SNO INTEGER PNO INTEGER Data Types in SQL The following is a list of some data types that are supported by SQL INTEGER signed fullword binary integer 31 bits precision SMALLINT signed halfword binary integer 15 bits precision DECIMAL p q signed packed decimal number of p digits precision with assumed q of them right to the decimal point 15 gt p gt qq 2 0 If q is omitted it is assumed to be 0 FLOAT signed doubleword floating point number CHAR n fixed length character string of length n VARCHAR n varying length character string of maximum length n Create Index Indices are used to speed up access to a relation If a relation R has an index on attribute A then we can retrieve all tuples t having t A a in time roughly proportional to the number of such tuples t rather than in time proportional to the size of
27. e in R and whose last k2 components form a tuple in S UNION U builds the set theoretic union of two tables Given the tables R and S both must have the same arity the union R U S is the set of tuples that are in R or S or both INTERSECT A builds the set theoretic intersection of two tables Given the tables R and S R US is the set of tuples that are in R and in S We again require that R and S have the same arity DIFFERENCE or builds the set difference of two tables Let R and S again be two tables with the same arity R S is the set of tuples in R but not in S JOIN ID connects two tables by their common attributes Let R be a table with the attributes A B and C and let S be a table with the attributes C D and E There is one attribute common to both relations the attribute C R S 6R A R B R C S D S E 6R C S C R x S What are we doing here We first calculate the Cartesian product R x S Then we select those tuples whose values for the common attribute C are equal 6R C S C Now we have a table that contains the attribute C two times and we correct this by projecting out the duplicate column Example 2 2 An Inner Join Let s have a look at the tables that are produced by evaluating the steps necessary for a join Let the following two tables be given R AIBIC S CIDIE 11213 3lalb 41516 6lcld 71819 First we calculate the Cartesian product R x S and get RxS A B R c s c D E
28. ebra vs Relational Calculus The relational algebra and the relational calculus have the same expressive power i e all queries that can be formulated using relational algebra can also be formulated using the relational calculus and vice versa This was first proved by E F Codd in 1972 This proof is based on an algorithm Codd s reduction algorithm by which an arbitrary expression of the relational calculus can be reduced to a semantically equivalent expression of relational algebra For a more detailed discussion on that refer to Date 1994 and Ullman 1988 It is sometimes said that languages based on the relational calculus are higher level or more declarative than languages based on relational algebra because the algebra partially specifies the order of operations while the calculus leaves it to a compiler or interpreter to determine the most efficient order of evaluation 13 Chapter 2 SOL The SQL Language As is the case with most modern relational languages SQL is based on the tuple relational calculus As a result every query that can be formulated using the tuple relational calculus or equivalently relational algebra can also be formulated using SQL There are however capabilities beyond the scope of relational algebra or calculus Here is a list of some additional features provided by SQL that are not part of relational algebra or calculus Commands for insertion deletion or modification of data Arithmetic
29. ems Vienna University of Technology Discusses SQL history and syntax and describes the addition of INTERSECT and EXCEPT constructs into Postgres Prepared as a Master s Thesis with the support of O Univ Prof Dr Georg Gottlob and Univ Ass Mag Katrin Seyr at Vienna University of Technology The Postgres95 User Manual Yu and Chen 1995 A Yu and J Chen The POSTGRES Group Sept 5 1995 University of California Berkeley CA 42 Bibliography Proceedings and Articles Partial indexing in POSTGRES research project Olson 1993 Nels Olson 1993 UCB Engin T7 49 1993 0676 University of California Berkeley CA A Unified Framework for Version Modeling Using Production Rules in a Database System Ong and Goh 1990 L Ong and J Goh April 1990 ERL Technical Memorandum M90 33 University of California Berkeley CA The Postgres Data Model Rowe and Stonebraker 1987 L Rowe and M Stonebraker Sept 1987 VLDB Conference Brighton England 1987 Generalized partial indexes http simon cs cornell edu home praveen papers partindex de95 ps Z P Seshadri and A Swami March 1995 Eleventh International Conference on Data Engineering 1995 Cat No 95CH35724 IEEE Computer Society Press The Design of Postgres Stonebraker and Rowe 1986 M Stonebraker and L Rowe May 1986 Conference on Management of Data Washington DC ACM SIGMOD 1986 The Design of the Postgres Rules System Stonebraker Hanson Hong 1
30. erage cost of all parts in table PART we use the following query SELECT AVG PRICE AS AVG PRICE FROM PART The result is AVG_ PRICE 16 Chapter 2 SOL If we want to know how many parts are stored in table PART we use the statement SELECT COUNT PNO FROM PART and get Aggregation by Groups SQL allows one to partition the tuples of a table into groups Then the aggregate operators described above can be applied to the groups i e the value of the aggregate operator is no longer calculated over all the values of the specified column but over all values of a group Thus the aggregate operator is evaluated individually for every group The partitioning of the tuples into groups is done by using the keywords GROUP BY followed by a list of attributes that define the groups If we have GROUP BY A1 Ak we partition the relation into groups such that two tuples are in the same group if and only if they agree on all the attributes Al Ak Example 2 6 Aggregates If we want to know how many parts are sold by every supplier we formulate the query SELECT S SNO S SNAME COUNT SE PNO FROM SUPPLIER S SELLS SE WHERE S SNO SE SNO GROUP BY S SNO S SNAME and get SNO SNAME COUNT Suse A A 1 Smith 2 2 Jones 1 3 Adams 2 4 Blake 3 Now let s have a look of what is happening here First the join of the tables SUPPLIER and SELLS is derived S SNO S SNAME SE PNO ESA E A 1 Smith le al Smith 2 2 Jones 4 3 Adam
31. eseeessereseseesrsrerrsserresesrsstsrtsrrsteeresrertnsrnresreetsseenrset 26 4 Getting Started omoomonmononnonoononocnoncononnoncononnoncononnoncononaoncononcononnoncononooncononooncononconconosoonoconecnosess 28 Setting Up Your Environ Menta cmrciorscdtcat e tarea icon ir s de 28 Starting the Interactive Monitor pPSQl oooconocnnonnnonononcnncnonocanonnnonncnononononnncnn cnn nonnncnncnnnonns 29 Manaping a Database ninio rt ba 29 Creating a Database nitro epi 29 Accessing a Databases sscssccsscc scssecsiesvcassasssesetiesthsshsssesvivehsssssssqesiassbessasvenesdesseeaeys 30 Destroying a Databases sa 31 5 The Query Language scssssssescssssecssesscosssosesossosssoseseassnasonssessvessosssssssessvessnesseessoessossooss 32 Interactive Moto diri 32 Eoi atea 0 Ee IN 32 Cre ting a New Cl sicos latino o la E E RE E S 33 Populating a Class with InsStancesS irsinin nono nocn nono no nn non nc nn nora reese 33 Querying a Classic cssecsssesesssssssaestesseuabasssadsctis sbesssansadstaspsspsustessisseassanssavaceeastystnasvedsaabsesee 33 Redirecting SELECT Queries iiien eooo neues Se eo Enee E tatu sey sens sens seeste NEE EER EES 34 Joms Between Classes ii bir 35 Updates escoltas tallo dato c it eseataati 36 Del A di 36 Using Agoresate FUNCUHONS ata tio deb 36 6 Advanced Postgres SQL Features csccssccssscscscccsssscccscssscssscsscssscsssesssssesscscssssssssessseees 38 Inercia incidir lanar idad EAE E E A EE 38
32. higher SELECT name altitude FROM cities WHERE altitude gt 500 name altitude Las Vegas 2174 Mariposa 1953 On the other hand to find the names of all cities including state capitals that are located at an altitude over 500ft the query is SELECT c name c altitude FROM cities c WHERE c altitude gt 500 38 Chapter 6 Advanced Postgres SOL Features which returns name altitude Las Vegas 2174 Mariposa 1953 Madison 845 Here the after cities indicates that the query should be run over cities and all classes below cities in the inheritance hierarchy Many of the commands that we have already discussed select update and delete support this notation as do others like alter Non Atomic Values One of the tenets of the relational model is that the attributes of a relation are atomic Postgres does not have this restriction attributes can themselves contain sub values that can be accessed from the query language For example you can create attributes that are arrays of base types Arrays Postgres allows attributes of an instance to be defined as fixed length or variable length multi dimensional arrays Arrays of any base type or user defined
33. i for each attribute Ai 1 lt i lt k where the values of the attributes are taken from We often write a relation scheme as R A1 A2 Ak Note A relation scheme is just a kind of template whereas a relation is an instance of a relation scheme The relation consists of tuples and can therefore be viewed as a table not so the relation scheme Domains vs Data Types We often talked about domains in the last section Recall that a domain is formally just a set of values e g the set of integers or the real numbers In terms of database systems we often talk of data types instead of domains When we define a table we have to make a decision about which attributes to include Additionally we have to decide which kind of data is going to be stored as attribute values For example the values of SNAME from the table SUPPLIER will be character strings whereas SNO will store integers We define this by assigning a data type to each attribute The type of SNAME will be VARCHAR 20 this is the SQL type for character strings of length lt 20 the type of SNO will be INTEGER With the assignment of a data type we also have selected a domain for an attribute The domain of SNAME is the set of all character strings of length lt 20 the domain of SNO is the set of all integer numbers Operations in the Relational Data Model In the previous section Relational Data Model Formalities we defined the mathematical notion of the relational
34. illed with tuples using the command INSERT INTO The syntax is INSERT INTO table name name of attr 1 name _ of attr 2 VALUES val_attr 1 val atti 2a e selly To insert the first tuple into the relation SUPPLIER from The Suppliers and Parts Database we use the following statement INSERT INTO SUPPLIER SNO SNAME CITY VALUES 1 Smith London To insert the first tuple into the relation SELLS we use INSERT INTO SELLS SNO PNO VALUES 1 1 23 Chapter 2 SOL Update To change one or more attribute values of tuples in a relation the UPDATE command is used The syntax is UPDATE table name SET name_of_attr_1 value _1 name _ of attr k value k WHERE condition To change the value of attribute PRICE of the part Screw in the relation PART we use UPDATE PART SET PRICE 15 WHERE PNAME Screw The new value of attribute PRICE of the tuple whose name is Screw is now 15 Delete To delete a tuple from a particular table use the command DELETE FROM The syntax is DELETE FROM table name WHERE condition To delete the supplier called Smith of the table SUPPLIER the following statement is used DELETE FROM SUPPLIER WHERE SNAME Smith System Catalogs In every SQL database system system catalogs are used to keep track of which tables views indexes etc are defined in the database These system catalogs can be queried as if they
35. ins are realized in SQL To join the three tables SUPPLIER PART and SELLS over their common attributes we formulate the following statement SELECT S SNAME P PNAME FROM SUPPLIER S PART P SELLS SE WHERE S SNO SE SNO AND P PNO SE PNO and get the following table as a result SNAME PNAME Patten tories aea Smith Screw Smith Nut Jones Cam Adams Screw Adams Bolt Blake Nut Blake Bolt Blake Cam In the FROM clause we introduced an alias name for every relation because there are common named attributes SNO and PNO among the relations Now we can distinguish between the common named attributes by simply prefixing the attribute name with the alias name followed by a dot The join is calculated in the same way as shown in An Inner Join First the Cartesian product SUPPLIER x PART x SELLS is derived Now only those tuples satisfying the conditions given in the WHERE clause are selected 1 e the common named attributes have to be equal Finally we project out all columns but S SNAME and P PNAME Aggregate Operators SQL provides aggregate operators e g AVG COUNT SUM MIN MAX that take the name of an attribute as an argument The value of the aggregate operator is calculated over all values of the specified attribute column of the whole table If groups are specified in the query the calculation is done only over the values of a group see next section Example 2 5 Aggregates If we want to know the av
36. ished which in turn starts a new backend server process and connects the frontend process to the new server From that point on the frontend process and the backend server communicate without intervention by the postmaster Hence the postmaster is always running waiting for requests whereas frontend and backend processes come and go The libpq library allows a single frontend to make multiple connections to backend processes However the frontend application is still a single threaded process Multithreaded frontend backend connections are not currently supported in libpq One implication of this architecture is that the postmaster and the backend always run on the same machine the database server while the frontend application may run anywhere You should keep this in mind because the files that can be accessed on a client machine may not be accessible or may only be accessed using a different filename on the database server machine You should also be aware that the postmaster and postgres servers run with the user id of the Postgres superuser Note that the Postgres superuser does not have to be a special user e g a user named postgres Furthermore the Postgres superuser should definitely not be the UNIX superuser root In any case all files relating to a database should belong to this Postgres superuser 26 Figure 3 1 How a connection is established a frontend sends request to postmaster via well known netwo
37. le PNO PNAME PRICE Using in the SELECT statement will deliver all attributes from the table If we want to retrieve only the attributes PNAME and PRICE from table PART we use the statement SELECT PNAME PRICE FROM PART WHERE PRICE gt 10 In this case the result is PNAME PRICE Sa 2e ee Bolt 15 Cam 25 Note that the SQL SELECT corresponds to the projection in relational algebra not to the selection see Relational Algebra for more details The qualifications in the WHERE clause can also be logically connected using the keywords OR AND and NOT SELECT PNAME PRICE FROM PART WHERE PNAME Bolt AND PRICE 0 OR PRICE lt 15 will lead to the result PNAME PRICE Ss Bolt 15 Arithmetic operations may be used in the target list and in the WHERE clause For example if we want to know how much it would cost if we take two pieces of a part we could use the following query SELECT PNAME PRICE 2 AS DOUBLE FROM PART WHERE PRICE 2 lt 50 and we get PNAME DOUBLE Siena PA Screw 20 Nut 16 Bolt 30 Note that the word DOUBLE after the keyword AS is the new title of the second column This technique can be used for every element of the target list to assign a new title to the resulting column This new title is often referred to as alias The alias cannot be used throughout the rest of the query 15 Chapter 2 SOL Joins The following example shows how jo
38. lity for it s behavior or performance However at the time of writing The author of this statement a volunteer on the Postgres support team since November 1996 is not aware of any problems in the Postgres code base related to time transitions around Jan 1 2000 Y2K The author of this statement is not aware of any reports of Y2K problems uncovered in regression testing or in other field use of recent or current versions of Postgres We might have expected to hear about problems if they existed given the installed base and the active participation of users on the support mailing lists To the best of the author s knowledge the assumptions Postgres makes about dates specified with a two digit year are documented in the current User s Guide http www postgresql org docs user datatype htm in the chapter on data types For two digit years the significant transition year is 1970 not 2000 e g 70 01 01 is interpreted as 1970 01 01 whereas 69 01 01 is interpreted as 2069 01 01 Any Y2K problems in the underlying OS related to obtaining the current time may propagate into apparent Y2K problems in Postgres Refer to The Gnu Project http www gnu org software year2000 html and The Perl Institute http language perl com news y2k html for further discussion of Y2K issues particularly as it relates to open source no fee software Copyrights and Trademarks PostgreSQL is Copyright 1996 9 by the PostgreSQL Global Developme
39. m the outer SELECT within the WHERE clause of the inner SELECT As described above the subquery is evaluated for every tuple from the outer query i e the value for S SNO is always taken from the actual tuple of the outer SELECT Union Intersect Except These operations calculate the union intersect and set theoretic difference of the tuples derived by two subqueries Example 2 9 Union Intersect Except The following query is an example for UNION SELECT S SNO S SNAME S CITY FROM SUPPLIER S WHERE S SNAME Jones UNION SELECT S SNO S SNAME S CITY FROM SUPPLIER S WHERE S SNAME Adams gives the result SNO SNAME CITY A Bee ane ae here a 2 Jones Paris 3 Adams Vienna Here an example for INTERSECT SELECT S SNO S SNAME S CITY 19 FROM SUPPLIER WHERE S SNO gt INTERSECT SELECT S SNO FROM SUPPLIER WHERE S SNO gt gives the result SNO 2 RUN S SNAME S CITY S 2 1 SNO SNAME Chapter 2 SOL CITY 2 Jones Paris The only tuple returned by both parts of the query is the one having Finally an example for EXCEPT SELECT S SNO FROM SUPPLIER WHERE S SNO gt EXCEPT SELECT S SNO FROM SUPPLIER WHERE S SNO gt S SNAME S CITY S 1 S SNAME S CITY S 3 gives the result SNO SNAME CITY AA A A 2 Jones Paris 3 Adams Vienna Data Definition There is a set of commands used for data definition included in the SQL language Create Tabl
40. model Now we know how the data can be stored using a relational data model but we do not know what to do with all these tables to retrieve something from the database yet For example somebody could ask for the names of all suppliers that sell the part Screw Therefore two rather different kinds of notations for expressing operations on relations have been defined The Relational Algebra which is an algebraic notation where queries are expressed by applying specialized operators to the relations The Relational Calculus which is a logical notation where queries are expressed by formulating some logical restrictions that the tuples in the answer must satisfy Relational Algebra The Relational Algebra was introduced by E F Codd in 1972 It consists of a set of operations on relations 10 Chapter 2 SOL SELECT 6 extracts tuples from a relation that satisfy a given restriction Let R be a table that contains an attribute A bA a R te R t A a where t denotes a tuple of R and t A denotes the value of attribute A of tuple t PROJECT 6 extracts specified attributes columns from a relation Let R be a relation that contains an attribute X 6X R t X te R where t X denotes the value of attribute X of tuple t PRODUCT x builds the Cartesian product of two relations Let R be a table with arity k1 and let S be a table with arity k2 R x S is the set of all k1 k2 tuples whose first k1 components form a tupl
41. n source descendant of this original Berkeley code Postgres95 is a derivative of the last official release of Postgres version 4 2 The code is now completely ANSI C and the code size has been trimmed by 25 There are a lot of internal changes that improve performance and code maintainability Postgres95 v1 0 x runs about 30 50 faster on the Wisconsin Benchmark compared to v4 2 Apart from bug fixes these are the major enhancements The query language Postquel has been replaced with SQL implemented in the server We do not yet support subqueries which can be imitated with user defined SQL functions Aggregates have been re implemented We also added support for GROUP BY The libpq interface is still available for C programs Chapter 1 Introduction In addition to the monitor program we provide a new program psql which supports GNU readline We added a new front end library libpgtcl that supports Tcl based clients A sample shell pgtclsh provides new Tcl commands to interface tcl programs with the Postgres95 backend The large object interface has been overhauled We kept Inversion large objects as the only mechanism for storing large objects This is not to be confused with the Inversion file system which has been removed The instance level rule system has been removed Rules are still available as rewrite rules A short tutorial introducing regular SQL features as well as those of ours is distributed with the s
42. n we look at the examples throughout Select we realize that the result of the queries is very often a set of tuples Most host languages are not designed to operate on sets so we need a mechanism to access every single tuple of the set of tuples returned by a SELECT statement This mechanism can be provided by declaring a cursor After that we can use the FETCH command to retrieve a tuple and set the cursor to the next tuple For a detailed discussion on embedded SQL refer to Date and Darwen 1997 Date 1994 or Ullman 1988 25 Chapter 3 Architecture Postgres Architectural Concepts Before we begin you should understand the basic Postgres system architecture Understanding how the parts of Postgres interact will make the next chapter somewhat clearer In database jargon Postgres uses a simple process per user client server model A Postgres session consists of the following cooperating UNIX processes programs A supervisory daemon process postmaster the user s frontend application e g the psql program and the one or more backend database servers the postgres process itself A single postmaster manages a given collection of databases on a single host Such a collection of databases is called an installation or site Frontend applications that wish to access a given database within an installation make calls to the library The library sends user requests over the network to the postmaster How a connection is establ
43. nally appeared as a part of Stefan Simkovics Master s Thesis Simkovics 1998 SQL has become the most popular relational query language The name SQL is an abbreviation for Structured Query Language In 1974 Donald Chamberlin and others defined the language SEQUEL Structured English Query Language at IBM Research This language was first implemented in an IBM prototype called SEQUEL XRM in 1974 75 In 1976 77 a revised version of SEQUEL called SEQUEL 2 was defined and the name was changed to SQL subsequently A new prototype called System R was developed by IBM in 1977 System R implemented a large subset of SEQUEL 2 now SQL and a number of changes were made to SQL during the project System R was installed in a number of user sites both internal IBM sites and also some selected customer sites Thanks to the success and acceptance of System R at those user sites IBM started to develop commercial products that implemented the SQL language based on the System R technology Over the next years IBM and also a number of other vendors announced SQL products such as SQL DS IBM DB2 IBM ORACLE Oracle Corp DG SQL Data General Corp and SYBASE Sybase Inc SQL is also an official standard now In 1982 the American National Standards Institute ANSI chartered its Database Committee X3H2 to develop a proposal for a standard relational language This proposal was ratified in 1986 and consisted essentially of the IBM dialect of SQL In
44. nt Group and is distributed under the terms of the Berkeley license Postgres95 is Copyright 1994 5 by the Regents of the University of California Permission to use copy modify and distribute this software and its documentation for any purpose Chapter 1 Introduction without fee and without a written agreement is hereby granted provided that the above copyright notice and this paragraph and the following two paragraphs appear in all copies In no event shall the University of California be liable to any party for direct indirect special incidental or consequential damages including lost profits arising out of the use of this software and its documentation even if the University of California has been advised of the possibility of such damage The University of California specifically disclaims any warranties including but not limited to the implied warranties of merchantability and fitness for a particular purpose The software provided hereunder is on an as is basis and the University of California has no obligations to provide maintainance support updates enhancements or modifications UNIX is a trademark of X Open Ltd Sun4 SPARC SunOS and Solaris are trademarks of Sun Microsystems Inc DEC DECstation Alpha AXP and ULTRIX are trademarks of Digital Equipment Corp PA RISC and HP UX are trademarks of Hewlett Packard Co OSF 1 is a trademark of the Open Software Foundation Chapter 2 SQL This chapter origi
45. ny particular set of installed Postgres binaries and databases The Postgres superuser is the user named postgres who owns the Postgres binaries and database files As the database superuser all protection mechanisms may be bypassed and any data accessed arbitrarily In addition the Postgres superuser is allowed to execute some support programs which are generally not available to all users Note that the Postgres superuser is not the same as the Unix superuser which will be referred to as root The superuser should have a non zero user identifier UID for security reasons The database administrator or DBA is the person who is responsible for installing Postgres with mechanisms to enforce a security policy for a site The DBA can add new users by the method described below and maintain a set of template databases for use by createdb The postmaster is the process that acts as a clearing house for requests to the Postgres system Frontend applications connect to the postmaster which keeps tracks of any system errors and communication between the backend processes The postmaster can take several command line arguments to tune its behavior However supplying arguments is necessary only if you intend to run multiple sites or a non default site The Postgres backend the actual executable program postgres may be executed directly from the user shell by the Postgres super user with the database name as an argument However doing this bypasses
46. ote machine you will need to set the PGHOST environment variable to the name of the database server machine The environment variable PGPORT may also have to be set The bottom line is this if you try to start an application program and it complains that it cannot connect to the postmaster you 28 Chapter 4 Getting Started should immediately consult your site administrator to make sure that your environment is properly set up Starting the Interactive Monitor psq l Assuming that your site administrator has properly started the postmaster process and authorized you to use the database you as a user may begin to start up applications As previously mentioned you should add usr local pgsql bin to your shell search path In most cases this is all you should have to do in terms of preparation As of Postgres v6 3 two different styles of connections are supported The site administrator will have chosen to allow TCP IP network connections or will have restricted database access to local same machine socket connections only These choices become significant if you encounter problems in connecting to a database If you get the following error message from a Postgres command such as psql or createdb o psql templatel Connection to database postgres failed connectDB failed Is the postmaster running and accepting connections at UNIX Socket on port 5432 or o psql h localhost templatel Connection to
47. ource code GNU make instead of BSD make is used for the build Also Postgres95 can be compiled with an unpatched gcc data alignment of doubles has been fixed PostgreSQL By 1996 it became clear that the name Postgres95 would not stand the test of time A new name PostgreSQL was chosen to reflect the relationship between original Postgres and the more recent versions with SQL capability At the same time the version numbering was reset to start at 6 0 putting the numbers back into the sequence originally begun by the Postgres Project The emphasis on development for the v1 0 x releases of Postgres95 was on stabilizing the backend code With the v6 x series of PostgreSQL the emphasis has shifted from identifying and understanding existing problems in the backend to augmenting features and capabilities although work continues in all areas Major enhancements include Important backend features including subselects defaults constraints and triggers have been implemented Additional SQL92 compliant language features have been added including primary keys quoted identifiers literal string type coersion type casting and binary and hexadecimal integer input Built in types have been improved including new wide range date time types and additional geometric type support Overall backend code speed has been increased by approximately 20 40 and backend startup time has decreased 80 since v6 0 was released About This
48. peration OSUPPLIER SNAME 6PART PNAME Screw SUPPLIER I SELLS J PART We call such an operation a query If we evaluate the above query against the our example tables The Suppliers and Parts Database we will obtain the following result SNAME 12 Chapter 2 SOL Relational Calculus The relational calculus is based on the first order logic There are two variants of the relational calculus The Domain Relational Calculus DRC where variables stand for components attributes of the tuples The Tuple Relational Calculus TRC where variables stand for tuples We want to discuss the tuple relational calculus only because it is the one underlying the most relational languages For a detailed discussion on DRC and also TRC see Date 1994 or Ullman 1988 Tuple Relational Calculus The queries used in TRC are of the following form x A F x where x is a tuple variable A is a set of attributes and F is a formula The resulting relation consists of all tuples t A that satisfy F t If we want to answer the question from example A Query Using Relational Algebra using TRC we formulate the following query x SNAME x e SUPPLIER nonumber J y e SELLS 3 z PART y SNO x SNO nonumber Z PNO y PNO Mmonumber z PNAME Screw nonumber Evaluating the query against the tables from The Suppliers and Parts Database again leads to the same result as in A Query Using Relational Algebra Relational Alg
49. pt underlying the relational model is the set theoretic relation which is a subset of the Cartesian product of a list of domains This set theoretic relation gives the model its name do not confuse it with the relationship from the Entity Relationship model Formally a domain is simply a set of values For example the set of integers is a domain Also the set of character strings of length 20 and the real numbers are examples of domains The Cartesian product of domains D1 D2 Dk written D1 x D2 x x Dk is the set of all k tuples v1 v2 vk such that v1 e D1 v1 e D1 vk e Dk For example when we have k 2 D1 0 1 and D2 a b c then D1 x D2 is 0 a 0 b 0 c 1 a 1 b 1 c A Relation is any subset of the Cartesian product of one or more domains R c D1 x D2 x x Dk For example 0 a 0 b 1 a is a relation it is in fact a subset of D1 x D2 mentioned above Chapter 2 SOL The members of a relation are called tuples Each relation of some Cartesian product D1 x D2 x X Dk is said to have arity k and is therefore a set of k tuples A relation can be viewed as a table as we already did remember The Suppliers and Parts Database where every tuple is represented by a row and every column corresponds to one component of a tuple Giving names called attributes to the columns leads to the definition of a relation scheme A relation scheme R is a finite set of attributes Al A2 Ak There is a domain D
50. rage managers an improved query executor and a rewritten rewrite rule system For the most part releases since then have focused on portability and reliability Postgres has been used to implement many different research and production applications These include a financial data analysis system a jet engine performance monitoring package an asteroid tracking database a medical information database and several geographic information systems Postgres has also been used as an educational tool at several universities Finally Illustra Information Technologies http www illustra com since merged into Informix http www informix com picked up the code and commercialized it Postgres became the primary data manager for the Sequoia 2000 http www sdsc edu 0 Parts_Collabs S2K s2k_home html scientific computing project in late 1992 Furthermore the size of the external user community nearly doubled during 1993 It became increasingly obvious that maintenance of the prototype code and support was taking up large amounts of time that should have been devoted to database research In an effort to reduce this support burden the project officially ended with Version 4 2 Postgres95 In 1994 Andrew Yu mailto ayu informix com and Jolly Chen http http cs berkeley edu jolly added a SQL language interpreter to Postgres and the code was subsequently released to the Web to find its own way in the world Postgres95 was a public domain ope
51. rk socket c frontend connected to backend server And multiple connections can be established d frontend connected to multiple backend servers SN SERVER Chapter 3 Architecture 27 Chapter 4 Getting Started How to begin work with Postgres for a new user Some of the steps required to use Postgres can be performed by any Postgres user and some must be done by the site database administrator This site administrator is the person who installed the software created the database directories and started the postmaster process This person does not have to be the UNIX superuser root or the computer system administrator a person can install and use Postgres without any special accounts or privileges If you are installing Postgres yourself then refer to the Administrator s Guide for instructions on installation and return to this guide when the installation is complete Throughout this manual any examples that begin with the character are commands that should be typed at the UNIX shell prompt Examples that begin with the character are commands in the Postgres query language Postgres SQL Setting Up Your Environment This section discusses how to set up your own environment so that you can use frontend applications We assume Postgres has already been successfully installed and started refer to the Administrator s Guide and the installation notes for how to install Postgres Postgres is a
52. s 1 3 Adams 3 4 Blake 2 4 Blake 3 4 Blake 4 Next we partition the tuples into groups by putting all tuples together that agree on both attributes S SNO and S SNAME S SNO S SNAME SE PNO 1 Smith 1 17 Chapter 2 SOL 2 2 Jones 4 3 Adams a 3 4 Blake 2 3 4 In our example we got four groups and now we can apply the aggregate operator COUNT to every group leading to the total result of the query given above Note that for the result of a query using GROUP BY and aggregate operators to make sense the attributes grouped by must also appear in the target list All further attributes not appearing in the GROUP BY clause can only be selected by using an aggregate function On the other hand you can not use aggregate functions on attributes appearing in the GROUP BY clause Having The HAVING clause works much like the WHERE clause and is used to consider only those groups satisfying the qualification given in the HAVING clause The expressions allowed in the HAVING clause must involve aggregate functions Every expression using only plain attributes belongs to the WHERE clause On the other hand every expression involving an aggregate function must be put to the HAVING clause Example 2 7 Having If we want only those suppliers selling more than one part we use the query SELECT S SNO S SNAME COUNT SE PNO FROM SUPPLIER S SELLS SE WHERE S SNO SE SNO GROUP BY S SNO S SNAME HAVING COUNT SE PNO gt 1
53. s as allowed by SQL92 Postgres SQL supports the usual SQL types int float real smallint char N varchar N date time and timestamp as well as other types of general utility and a rich set of geometric types As we will see later Postgres can be customized with an arbitrary number of user defined data types Consequently type names are not syntactical keywords except where required to support special cases in the SQL92 standard So far the Postgres create command looks exactly like the command used to create a table in a traditional relational system However we will presently see that classes have properties that are extensions of the relational model Populating a Class with Instances The insert statement is used to populate a class with instances INSERT INTO weather VALUES San Francisco 46 50 0 25 11 27 1994 You can also use the copy command to perform load large amounts of data from flat ASCII files This is usually faster because the data is read or written as a single atomic transaction directly to or from the target table An example would be COPY INTO weather FROM home user weather txt USING DELIMITERS ess where the path name for the source file must be available to the backend server machine not the client since the backend server reads the file directly Querying a Class The weather class can be queried with normal relational selection and projection queries A SQL select statement is used to
54. sql The i command read in queries from the specified files The s option puts you in single step mode which pauses before sending a query to the backend Queries in this section are in the file basics sql psql has a variety of d commands for showing system information Consult these commands for more details for a listing type 1 at the psql prompt Concepts The fundamental notion in Postgres is that of a class which is a named collection of object instances Each instance has the same collection of named attributes and each attribute is of a specific type Furthermore each instance has a permanent object identifier OID that is unique throughout the installation Because SQL syntax refers to tables we will use the terms table and class interchangeably Likewise an SQL row is an instance and SQL columns are attributes As previously discussed classes are grouped into databases and a collection of databases managed by a single postmaster process constitutes an installation or site 32 Chapter 5 The Query Language Creating a New Class You can create a new class by specifying the class name along with all attribute names and their types CREATE TABLE weather city varchar 80 temp_lo Int low temperature temp hi int high temperature prep real precipitation date date Note that both keywords and identifiers are case insensitive identifiers can become case sensitive by surrounding them with double quote
55. ssssiscussssssstessessveessassseisbescnesassevbucs epebsosesdbatipstsaseas ssebabapsssseeesese 13 Tuple Relational Calculus ooooonconocnnonononocononononancnnncnnnnancnnn conc non conc noc noco no cnn con nono 13 Relational Algebra vs Relational Calculus oonocnicnnnnncnnncnoonconnconoconcnnnconoconocnnornss 13 The SQL Lan ua ge escitas lion scales insti 14 Selecta s lina 14 Simple Selec ui ii resi 14 TOMOS ie ler pacien rsisl 16 Aggregate Operators mooier ea re eas e aea E eoa ae nn cono coronan cone cn neon aran Es 16 Aggregation by GTOUPS ccooonocnncnconnnoncnoncnnncnnconnconoco noc nonno cono cn nono nc onncnnccnnconncnnos 17 A n ae e easuecs basset EE A EEE E E EE AE S 18 SUDQUETIOS 2 535 Ghia aa E 18 Union Intersect POEP istics ceesiicsccsheeschsvesnstosetvocvwnces uaesuopenseunestocbanesents conte 19 Data Definition renien o A E eaceageosudl gic E eet Snatel weoveteeb beats 20 Create Table usted HS phe Ae A ea ei Ea Se iets 20 Data Types M SOL iii caia lr ies 21 Create decicion 21 Create View isd tes eked Rd Ahi RS 22 Drop Table Drop Index Drop View es ce ceecesseceeeeeceeceeneeceseeeseeceereeeaeeeeee 22 Data Manipulacion satreetie eres ee tom ESERE 23 Insert Intec set echass eid ee el OS ed 23 E 24 Delicia it A rs 24 System Catalogs cin ad 24 Embedded SOL e es e e es 24 OS eksos aoo ositpata sesat s otse e ttes SESS te SeA SEESE ETE SSES SESE EES 26 Postgres Architectural Concepts es
56. stgres allows you to create any number of databases at a given site and you automatically become the database administrator of the database you just created Database names must have an alphabetic first character and are limited to 32 characters in length Not every user has authorization to become a database administrator If Postgres refuses to create databases for you then the site administrator needs to grant you permission to create databases Consult your site administrator if this occurs Accessing a Database Once you have constructed a database you can access it by running the Postgres terminal monitor programs e g psql which allows you to interactively enter edit and execute SQL commands writing a C program using the LIBPQ subroutine library This allows you to submit SQL commands from C and get answers and status messages back to your program This interface is discussed further in The PostgreSQL Programmer s Guide You might want to start up psql to try out the examples in this manual It can be activated for the mydb database by typing the command o psql mydb You will be greeted with the following message Welcome to the POSTGRESQL interactive sql monitor Please read the file COPYRIGHT for copyright terms of POSTGRESQL type for help on slash commands type q to quit type g or terminate with semicolon to execute query You are currently connected to the database templatel mydb gt This prompt indi
57. to as object relational Note that this is distinct from those referred to as object oriented which in general are not as well suited to supporting the traditional relational database languages So although Postgres has some object oriented features it is firmly in the relational database world In fact some commercial databases have recently incorporated features pioneered by Postgres Chapter 1 Introduction A Short History of Postgres The Berkeley Postgres Project Implementation of the Postgres DBMS began in 1986 The initial concepts for the system were presented in The Design of Postgres and the definition of the initial data model appeared in The Postgres Data Model The design of the rule system at that time was described in The Design of the Postgres Rules System The rationale and architecture of the storage manager were detailed in The Postgres Storage System Postgres has undergone several major releases since then The first demoware system became operational in 1987 and was shown at the 1988 ACM SIGMOD Conference We released Version 1 described in The Implementation of Postgres to a few external users in June 1989 In response to a critique of the first rule system A Commentary on the Postgres Rules System the rule system was redesigned On Rules Procedures Caching and Views in Database Systems and Version 2 was released in June 1990 with the new rule system Version 3 appeared in 1991 and added support for multiple sto
58. uments address both general issues and some platform specific issues READMEs README files are available for some contributed packages Web Site The Postgres postgresql org web site has some information not appearing in the distribution There is a mhonarc catalog of mailing list traffic which is a rich resource for many topics Chapter 1 Introduction Mailing Lists The Postgres Questions mailto questions O postgresql org mailing list is a good place to have user questions answered Other mailing lists are available consult the web page for details Yourself Postgres is an open source product As such it depends on the user community for ongoing support As you begin to use Postgres you will rely on others for help either through the documentation or through the mailing lists Consider contributing your knowledge back If you learn something which is not in the documentation write it up and contribute it If you add features to the code contribute it Even those without a lot of experience can provide corrections and minor changes in the documentation and that is a good way to start The Postgres Documentation mailto docs postgresql org mailing list is the place to get going Terminology In the following documentation site may be interpreted as the host machine on which Postgres is installed Since it is possible to install more than one set of Postgres databases on a single host this term more precisely denotes a
59. view is created It is just stored in the system catalogs and is executed whenever a query against the view is made Let the following view definition be given we use the tables from The Suppliers and Parts Database again CREATE VIEW London Suppliers AS SELECT S SNAME P PNAME FROM SUPPLIER S PART P SELLS SE WHERE S SNO SE SNO AND P PNO SE PNO AND S CITY London Now we can use this virtual relation London_Suppliers as if it were another base table SELECT FROM London Suppliers WHERE P PNAME Screw which will return the following table SNAME PNAME Smith Screw To calculate this result the database system has to do a hidden access to the base tables SUPPLIER SELLS and PART first It does so by executing the query given in the view definition against those base tables After that the additional qualifications given in the query against the view can be applied to obtain the resulting table Drop Table Drop Index Drop View To destroy a table including all tuples stored in that table the DROP TABLE command is used 22 Chapter 2 SOL DROP TABLE table name To destroy the SUPPLIER table use the following statement DROP TABLE SUPPLIER The DROP INDEX command is used to destroy an index DROP INDEX index name Finally to destroy a given view use the command DROP VIEW DROP VIEW view name Data Manipulation Insert Into Once a table is created see Create Table it can be f
60. were normal relations For example there is one catalog used for the definition of views This catalog stores the query from the view definition Whenever a query against a view is made the system first gets the view definition query out of the catalog and materializes the view before proceeding with the user query see SIM98 for a more detailed description For more information about system catalogs refer to DATE Embedded SQL In this section we will sketch how SQL can be embedded into a host language e g C There are two main reasons why we want to use SQL from a host language 24 Chapter 2 SOL There are queries that cannot be formulated using pure SQL i e recursive queries To be able to perform such queries we need a host language with a greater expressive power than SQL We simply want to access a database from some application that is written in the host language e g a ticket reservation system with a graphical user interface is written in C and the information about which tickets are still left is stored in a database that can be accessed using embedded SQL A program using embedded SQL in a host language consists of statements of the host language and of embedded SQL ESQL statements Every ESQL statement begins with the keywords EXEC SQL The ESQL statements are transformed to statements of the host language by a precompiler which usually inserts calls to library routines that perform the various SQL commands Whe

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