codekingpro/portable-devtools

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>CREATE TRANSFORM</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 Vsnapshot" /><link rel="prev" href="sql-createtstemplate.html" title="CREATE TEXT SEARCH TEMPLATE" /><link rel="next" href="sql-createtrigger.html" title="CREATE TRIGGER" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">CREATE TRANSFORM</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="sql-createtstemplate.html" title="CREATE TEXT SEARCH TEMPLATE">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="sql-commands.html" title="SQL Commands">Up</a></td><th width="60%" align="center">SQL Commands</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 16.3 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="sql-createtrigger.html" title="CREATE TRIGGER">Next</a></td></tr></table><hr /></div><div class="refentry" id="SQL-CREATETRANSFORM"><div class="titlepage"></div><a id="id-1.9.3.92.1" class="indexterm"></a><div class="refnamediv"><h2><span class="refentrytitle">CREATE TRANSFORM</span></h2><p>CREATE TRANSFORM — define a new transform</p></div><div class="refsynopsisdiv"><h2>Synopsis</h2><pre class="synopsis">3CREATE [ OR REPLACE ] TRANSFORM FOR <em class="replaceable"><code>type_name</code></em> LANGUAGE <em class="replaceable"><code>lang_name</code></em> (4    FROM SQL WITH FUNCTION <em class="replaceable"><code>from_sql_function_name</code></em> [ (<em class="replaceable"><code>argument_type</code></em> [, ...]) ],5    TO SQL WITH FUNCTION <em class="replaceable"><code>to_sql_function_name</code></em> [ (<em class="replaceable"><code>argument_type</code></em> [, ...]) ]6);7</pre></div><div class="refsect1" id="SQL-CREATETRANSFORM-DESCRIPTION"><h2>Description</h2><p>8   <code class="command">CREATE TRANSFORM</code> defines a new transform.9   <code class="command">CREATE OR REPLACE TRANSFORM</code> will either create a new10   transform, or replace an existing definition.11  </p><p>12   A transform specifies how to adapt a data type to a procedural language.13   For example, when writing a function in PL/Python using14   the <code class="type">hstore</code> type, PL/Python has no prior knowledge how to15   present <code class="type">hstore</code> values in the Python environment.  Language16   implementations usually default to using the text representation, but that17   is inconvenient when, for example, an associative array or a list would be18   more appropriate.19  </p><p>20   A transform specifies two functions:21   </p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>22      A <span class="quote">“<span class="quote">from SQL</span>”</span> function that converts the type from the SQL23      environment to the language.  This function will be invoked on the24      arguments of a function written in the language.25     </p></li><li class="listitem"><p>26      A <span class="quote">“<span class="quote">to SQL</span>”</span> function that converts the type from the27      language to the SQL environment.  This function will be invoked on the28      return value of a function written in the language.29     </p></li></ul></div><p>30   It is not necessary to provide both of these functions.  If one is not31   specified, the language-specific default behavior will be used if32   necessary.  (To prevent a transformation in a certain direction from33   happening at all, you could also write a transform function that always34   errors out.)35  </p><p>36   To be able to create a transform, you must own and37   have <code class="literal">USAGE</code> privilege on the type, have38   <code class="literal">USAGE</code> privilege on the language, and own and39   have <code class="literal">EXECUTE</code> privilege on the from-SQL and to-SQL40   functions, if specified.41  </p></div><div class="refsect1" id="id-1.9.3.92.6"><h2>Parameters</h2><div class="variablelist"><dl class="variablelist"><dt><span class="term"><em class="replaceable"><code>type_name</code></em></span></dt><dd><p>42       The name of the data type of the transform.43      </p></dd><dt><span class="term"><em class="replaceable"><code>lang_name</code></em></span></dt><dd><p>44       The name of the language of the transform.45      </p></dd><dt><span class="term"><code class="literal"><em class="replaceable"><code>from_sql_function_name</code></em>[(<em class="replaceable"><code>argument_type</code></em> [, ...])]</code></span></dt><dd><p>46       The name of the function for converting the type from the SQL47       environment to the language.  It must take one argument of48       type <code class="type">internal</code> and return type <code class="type">internal</code>.  The49       actual argument will be of the type for the transform, and the function50       should be coded as if it were.  (But it is not allowed to declare an51       SQL-level function returning <code class="type">internal</code> without at52       least one argument of type <code class="type">internal</code>.)  The actual return53       value will be something specific to the language implementation.54       If no argument list is specified, the function name must be unique in55       its schema.56      </p></dd><dt><span class="term"><code class="literal"><em class="replaceable"><code>to_sql_function_name</code></em>[(<em class="replaceable"><code>argument_type</code></em> [, ...])]</code></span></dt><dd><p>57       The name of the function for converting the type from the language to58       the SQL environment.  It must take one argument of type59       <code class="type">internal</code> and return the type that is the type for the60       transform.  The actual argument value will be something specific to the61       language implementation.62       If no argument list is specified, the function name must be unique in63       its schema.64      </p></dd></dl></div></div><div class="refsect1" id="SQL-CREATETRANSFORM-NOTES"><h2>Notes</h2><p>65   Use <a class="link" href="sql-droptransform.html" title="DROP TRANSFORM"><code class="command">DROP TRANSFORM</code></a> to remove transforms.66  </p></div><div class="refsect1" id="SQL-CREATETRANSFORM-EXAMPLES"><h2>Examples</h2><p>67   To create a transform for type <code class="type">hstore</code> and language68   <code class="literal">plpython3u</code>, first set up the type and the language:69</p><pre class="programlisting">70CREATE TYPE hstore ...;71 72CREATE EXTENSION plpython3u;73</pre><p>74   Then create the necessary functions:75</p><pre class="programlisting">76CREATE FUNCTION hstore_to_plpython(val internal) RETURNS internal77LANGUAGE C STRICT IMMUTABLE78AS ...;79 80CREATE FUNCTION plpython_to_hstore(val internal) RETURNS hstore81LANGUAGE C STRICT IMMUTABLE82AS ...;83</pre><p>84   And finally create the transform to connect them all together:85</p><pre class="programlisting">86CREATE TRANSFORM FOR hstore LANGUAGE plpython3u (87    FROM SQL WITH FUNCTION hstore_to_plpython(internal),88    TO SQL WITH FUNCTION plpython_to_hstore(internal)89);90</pre><p>91   In practice, these commands would be wrapped up in an extension.92  </p><p>93   The <code class="filename">contrib</code> section contains a number of extensions94   that provide transforms, which can serve as real-world examples.95  </p></div><div class="refsect1" id="SQL-CREATETRANSFORM-COMPAT"><h2>Compatibility</h2><p>96   This form of <code class="command">CREATE TRANSFORM</code> is a97   <span class="productname">PostgreSQL</span> extension.  There is a <code class="command">CREATE98   TRANSFORM</code> command in the <acronym class="acronym">SQL</acronym> standard, but it99   is for adapting data types to client languages.  That usage is not supported100   by <span class="productname">PostgreSQL</span>.101  </p></div><div class="refsect1" id="SQL-CREATETRANSFORM-SEEALSO"><h2>See Also</h2><p>102   <a class="xref" href="sql-createfunction.html" title="CREATE FUNCTION"><span class="refentrytitle">CREATE FUNCTION</span></a>,103   <a class="xref" href="sql-createlanguage.html" title="CREATE LANGUAGE"><span class="refentrytitle">CREATE LANGUAGE</span></a>,104   <a class="xref" href="sql-createtype.html" title="CREATE TYPE"><span class="refentrytitle">CREATE TYPE</span></a>,105   <a class="xref" href="sql-droptransform.html" title="DROP TRANSFORM"><span class="refentrytitle">DROP TRANSFORM</span></a>106  </p></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="sql-createtstemplate.html" title="CREATE TEXT SEARCH TEMPLATE">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="sql-commands.html" title="SQL Commands">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="sql-createtrigger.html" title="CREATE TRIGGER">Next</a></td></tr><tr><td width="40%" align="left" valign="top">CREATE TEXT SEARCH TEMPLATE </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 16.3 Documentation">Home</a></td><td width="40%" align="right" valign="top"> CREATE TRIGGER</td></tr></table></div></body></html>