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diff --git a/doc/src/sgml/html/catalog-pg-cast.html b/doc/src/sgml/html/catalog-pg-cast.html new file mode 100644 index 0000000..84762e5 --- /dev/null +++ b/doc/src/sgml/html/catalog-pg-cast.html @@ -0,0 +1,86 @@ +<?xml version="1.0" encoding="UTF-8" standalone="no"?> +<!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>53.10. pg_cast</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="catalog-pg-auth-members.html" title="53.9. pg_auth_members" /><link rel="next" href="catalog-pg-class.html" title="53.11. pg_class" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">53.10. <code class="structname">pg_cast</code></th></tr><tr><td width="10%" align="left"><a accesskey="p" href="catalog-pg-auth-members.html" title="53.9. pg_auth_members">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="catalogs.html" title="Chapter 53. System Catalogs">Up</a></td><th width="60%" align="center">Chapter 53. System Catalogs</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 15.5 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="catalog-pg-class.html" title="53.11. pg_class">Next</a></td></tr></table><hr /></div><div class="sect1" id="CATALOG-PG-CAST"><div class="titlepage"><div><div><h2 class="title" style="clear: both">53.10. <code class="structname">pg_cast</code></h2></div></div></div><a id="id-1.10.4.12.2" class="indexterm"></a><p> + The catalog <code class="structname">pg_cast</code> stores data type conversion + paths, both built-in and user-defined. + </p><p> + It should be noted that <code class="structname">pg_cast</code> does not represent + every type conversion that the system knows how to perform; only those that + cannot be deduced from some generic rule. For example, casting between a + domain and its base type is not explicitly represented in + <code class="structname">pg_cast</code>. Another important exception is that + <span class="quote">“<span class="quote">automatic I/O conversion casts</span>”</span>, those performed using a data + type's own I/O functions to convert to or from <code class="type">text</code> or other + string types, are not explicitly represented in + <code class="structname">pg_cast</code>. + </p><div class="table" id="id-1.10.4.12.5"><p class="title"><strong>Table 53.10. <code class="structname">pg_cast</code> Columns</strong></p><div class="table-contents"><table class="table" summary="pg_cast Columns" border="1"><colgroup><col /></colgroup><thead><tr><th class="catalog_table_entry"><p class="column_definition"> + Column Type + </p> + <p> + Description + </p></th></tr></thead><tbody><tr><td class="catalog_table_entry"><p class="column_definition"> + <code class="structfield">oid</code> <code class="type">oid</code> + </p> + <p> + Row identifier + </p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition"> + <code class="structfield">castsource</code> <code class="type">oid</code> + (references <a class="link" href="catalog-pg-type.html" title="53.64. pg_type"><code class="structname">pg_type</code></a>.<code class="structfield">oid</code>) + </p> + <p> + OID of the source data type + </p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition"> + <code class="structfield">casttarget</code> <code class="type">oid</code> + (references <a class="link" href="catalog-pg-type.html" title="53.64. pg_type"><code class="structname">pg_type</code></a>.<code class="structfield">oid</code>) + </p> + <p> + OID of the target data type + </p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition"> + <code class="structfield">castfunc</code> <code class="type">oid</code> + (references <a class="link" href="catalog-pg-proc.html" title="53.39. pg_proc"><code class="structname">pg_proc</code></a>.<code class="structfield">oid</code>) + </p> + <p> + The OID of the function to use to perform this cast. Zero is + stored if the cast method doesn't require a function. + </p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition"> + <code class="structfield">castcontext</code> <code class="type">char</code> + </p> + <p> + Indicates what contexts the cast can be invoked in. + <code class="literal">e</code> means only as an explicit cast (using + <code class="literal">CAST</code> or <code class="literal">::</code> syntax). + <code class="literal">a</code> means implicitly in assignment + to a target column, as well as explicitly. + <code class="literal">i</code> means implicitly in expressions, as well as the + other cases. + </p></td></tr><tr><td class="catalog_table_entry"><p class="column_definition"> + <code class="structfield">castmethod</code> <code class="type">char</code> + </p> + <p> + Indicates how the cast is performed. + <code class="literal">f</code> means that the function specified in the <code class="structfield">castfunc</code> field is used. + <code class="literal">i</code> means that the input/output functions are used. + <code class="literal">b</code> means that the types are binary-coercible, thus no conversion is required. + </p></td></tr></tbody></table></div></div><br class="table-break" /><p> + The cast functions listed in <code class="structname">pg_cast</code> must + always take the cast source type as their first argument type, and + return the cast destination type as their result type. A cast + function can have up to three arguments. The second argument, + if present, must be type <code class="type">integer</code>; it receives the type + modifier associated with the destination type, or -1 + if there is none. The third argument, + if present, must be type <code class="type">boolean</code>; it receives <code class="literal">true</code> + if the cast is an explicit cast, <code class="literal">false</code> otherwise. + </p><p> + It is legitimate to create a <code class="structname">pg_cast</code> entry + in which the source and target types are the same, if the associated + function takes more than one argument. Such entries represent + <span class="quote">“<span class="quote">length coercion functions</span>”</span> that coerce values of the type + to be legal for a particular type modifier value. + </p><p> + When a <code class="structname">pg_cast</code> entry has different source and + target types and a function that takes more than one argument, it + represents converting from one type to another and applying a length + coercion in a single step. When no such entry is available, coercion + to a type that uses a type modifier involves two steps, one to + convert between data types and a second to apply the modifier. + </p></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="catalog-pg-auth-members.html" title="53.9. pg_auth_members">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="catalogs.html" title="Chapter 53. System Catalogs">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="catalog-pg-class.html" title="53.11. pg_class">Next</a></td></tr><tr><td width="40%" align="left" valign="top">53.9. <code class="structname">pg_auth_members</code> </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 15.5 Documentation">Home</a></td><td width="40%" align="right" valign="top"> 53.11. <code class="structname">pg_class</code></td></tr></table></div></body></html>
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