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  1. <?xml version="1.0" encoding="UTF-8" standalone="no"?>

  2. <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>42.1. Overview</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets V1.79.1" /><link rel="prev" href="plpgsql.html" title="Chapter 42. PL/pgSQL - SQL Procedural Language" /><link rel="next" href="plpgsql-structure.html" title="42.2. Structure of PL/pgSQL" /></head><body><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">42.1. Overview</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="plpgsql.html" title="Chapter 42. PL/pgSQL - SQL Procedural Language">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="plpgsql.html" title="Chapter 42. PL/pgSQL - SQL Procedural Language">Up</a></td><th width="60%" align="center">Chapter 42. <span xmlns="http://www.w3.org/1999/xhtml" class="application">PL/pgSQL</span> - <acronym xmlns="http://www.w3.org/1999/xhtml" class="acronym">SQL</acronym> Procedural Language</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 12.4 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="plpgsql-structure.html" title="42.2. Structure of PL/pgSQL">Next</a></td></tr></table><hr></hr></div><div class="sect1" id="PLPGSQL-OVERVIEW"><div class="titlepage"><div><div><h2 class="title" style="clear: both">42.1. Overview</h2></div></div></div><div class="toc"><dl class="toc"><dt><span class="sect2"><a href="plpgsql-overview.html#PLPGSQL-ADVANTAGES">42.1.1. Advantages of Using <span class="application">PL/pgSQL</span></a></span></dt><dt><span class="sect2"><a href="plpgsql-overview.html#PLPGSQL-ARGS-RESULTS">42.1.2. Supported Argument and Result Data Types</a></span></dt></dl></div><p>

  3.   <span class="application">PL/pgSQL</span> is a loadable procedural

  4.   language for the <span class="productname">PostgreSQL</span> database

  5.   system.  The design goals of <span class="application">PL/pgSQL</span> were to create

  6.   a loadable procedural language that

  7. 

  8.     </p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>

  9.        can be used to create functions and triggers,

  10.       </p></li><li class="listitem"><p>

  11.        adds control structures to the <acronym class="acronym">SQL</acronym> language,

  12.       </p></li><li class="listitem"><p>

  13.        can perform complex computations,

  14.       </p></li><li class="listitem"><p>

  15.        inherits all user-defined types, functions, and operators,

  16.       </p></li><li class="listitem"><p>

  17.        can be defined to be trusted by the server,

  18.       </p></li><li class="listitem"><p>

  19.        is easy to use.

  20.       </p></li></ul></div><p>

  21.    </p><p>

  22.     Functions created with <span class="application">PL/pgSQL</span> can be

  23.     used anywhere that built-in functions could be used.

  24.     For example, it is possible to

  25.     create complex conditional computation functions and later use

  26.     them to define operators or use them in index expressions.

  27.    </p><p>

  28.     In <span class="productname">PostgreSQL</span> 9.0 and later,

  29.     <span class="application">PL/pgSQL</span> is installed by default.

  30.     However it is still a loadable module, so especially security-conscious

  31.     administrators could choose to remove it.

  32.    </p><div class="sect2" id="PLPGSQL-ADVANTAGES"><div class="titlepage"><div><div><h3 class="title">42.1.1. Advantages of Using <span class="application">PL/pgSQL</span></h3></div></div></div><p>

  33.      <acronym class="acronym">SQL</acronym> is the language <span class="productname">PostgreSQL</span>

  34.      and most other relational databases use as query language. It's

  35.      portable and easy to learn. But every <acronym class="acronym">SQL</acronym>

  36.      statement must be executed individually by the database server.

  37.     </p><p>

  38.      That means that your client application must send each query to

  39.      the database server, wait for it to be processed, receive and

  40.      process the results, do some computation, then send further

  41.      queries to the server.  All this incurs interprocess

  42.      communication and will also incur network overhead if your client

  43.      is on a different machine than the database server.

  44.     </p><p>

  45.      With <span class="application">PL/pgSQL</span> you can group a block of

  46.      computation and a series of queries <span class="emphasis"><em>inside</em></span>

  47.      the database server, thus having the power of a procedural

  48.      language and the ease of use of SQL, but with considerable

  49.      savings of client/server communication overhead.

  50.     </p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p> Extra round trips between

  51.      client and server are eliminated </p></li><li class="listitem"><p> Intermediate results that the client does not

  52.      need do not have to be marshaled or transferred between server

  53.      and client </p></li><li class="listitem"><p> Multiple rounds of query

  54.      parsing can be avoided </p></li></ul></div><p> This can result in a considerable performance increase as

  55.     compared to an application that does not use stored functions.

  56.     </p><p>

  57.      Also, with <span class="application">PL/pgSQL</span> you can use all

  58.      the data types, operators and functions of SQL.

  59.     </p></div><div class="sect2" id="PLPGSQL-ARGS-RESULTS"><div class="titlepage"><div><div><h3 class="title">42.1.2. Supported Argument and Result Data Types</h3></div></div></div><p>

  60.      Functions written in <span class="application">PL/pgSQL</span> can accept

  61.      as arguments any scalar or array data type supported by the server,

  62.      and they can return a result of any of these types.  They can also

  63.      accept or return any composite type (row type) specified by name.

  64.      It is also possible to declare a <span class="application">PL/pgSQL</span>

  65.      function as accepting <code class="type">record</code>, which means that any

  66.      composite type will do as input, or

  67.      as returning <code class="type">record</code>, which means that the result

  68.      is a row type whose columns are determined by specification in the

  69.      calling query, as discussed in <a class="xref" href="queries-table-expressions.html#QUERIES-TABLEFUNCTIONS" title="7.2.1.4. Table Functions">Section 7.2.1.4</a>.

  70.     </p><p>

  71.      <span class="application">PL/pgSQL</span> functions can be declared to accept a variable

  72.      number of arguments by using the <code class="literal">VARIADIC</code> marker.  This

  73.      works exactly the same way as for SQL functions, as discussed in

  74.      <a class="xref" href="xfunc-sql.html#XFUNC-SQL-VARIADIC-FUNCTIONS" title="37.5.5. SQL Functions with Variable Numbers of Arguments">Section 37.5.5</a>.

  75.     </p><p>

  76.      <span class="application">PL/pgSQL</span> functions can also be declared to accept

  77.      and return the polymorphic types

  78.      <code class="type">anyelement</code>, <code class="type">anyarray</code>, <code class="type">anynonarray</code>,

  79.      <code class="type">anyenum</code>, and <code class="type">anyrange</code>.  The actual

  80.      data types handled by a polymorphic function can vary from call to

  81.      call, as discussed in <a class="xref" href="extend-type-system.html#EXTEND-TYPES-POLYMORPHIC" title="37.2.5. Polymorphic Types">Section 37.2.5</a>.

  82.      An example is shown in <a class="xref" href="plpgsql-declarations.html#PLPGSQL-DECLARATION-PARAMETERS" title="42.3.1. Declaring Function Parameters">Section 42.3.1</a>.

  83.     </p><p>

  84.      <span class="application">PL/pgSQL</span> functions can also be declared to return

  85.      a <span class="quote">“<span class="quote">set</span>”</span> (or table) of any data type that can be returned as

  86.      a single instance.  Such a function generates its output by executing

  87.      <code class="command">RETURN NEXT</code> for each desired element of the result

  88.      set, or by using <code class="command">RETURN QUERY</code> to output the result of

  89.      evaluating a query.

  90.     </p><p>

  91.      Finally, a <span class="application">PL/pgSQL</span> function can be declared to return

  92.      <code class="type">void</code> if it has no useful return value.  (Alternatively, it

  93.      could be written as a procedure in that case.)

  94.     </p><p>

  95.      <span class="application">PL/pgSQL</span> functions can also be declared with output

  96.      parameters in place of an explicit specification of the return type.

  97.      This does not add any fundamental capability to the language, but

  98.      it is often convenient, especially for returning multiple values.

  99.      The <code class="literal">RETURNS TABLE</code> notation can also be used in place

  100.      of <code class="literal">RETURNS SETOF</code>.

  101.     </p><p>

  102.      Specific examples appear in

  103.      <a class="xref" href="plpgsql-declarations.html#PLPGSQL-DECLARATION-PARAMETERS" title="42.3.1. Declaring Function Parameters">Section 42.3.1</a> and

  104.      <a class="xref" href="plpgsql-control-structures.html#PLPGSQL-STATEMENTS-RETURNING" title="42.6.1. Returning From a Function">Section 42.6.1</a>.

  105.     </p></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="plpgsql.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="plpgsql.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="plpgsql-structure.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter 42. <span class="application">PL/pgSQL</span> - <acronym class="acronym">SQL</acronym> Procedural Language </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> 42.2. Structure of <span class="application">PL/pgSQL</span></td></tr></table></div></body></html>
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