diff options
Diffstat (limited to 'doc/src/sgml/ref')
| -rw-r--r-- | doc/src/sgml/ref/create_cast.sgml | 38 |
1 files changed, 29 insertions, 9 deletions
diff --git a/doc/src/sgml/ref/create_cast.sgml b/doc/src/sgml/ref/create_cast.sgml index 080f31832d2..c771d22ad94 100644 --- a/doc/src/sgml/ref/create_cast.sgml +++ b/doc/src/sgml/ref/create_cast.sgml @@ -1,4 +1,4 @@ -<!-- $PostgreSQL: pgsql/doc/src/sgml/ref/create_cast.sgml,v 1.29 2008/07/30 21:23:17 tgl Exp $ --> +<!-- $PostgreSQL: pgsql/doc/src/sgml/ref/create_cast.sgml,v 1.30 2008/10/31 08:39:20 heikki Exp $ --> <refentry id="SQL-CREATECAST"> <refmeta> @@ -24,6 +24,10 @@ CREATE CAST (<replaceable>sourcetype</replaceable> AS <replaceable>targettype</r CREATE CAST (<replaceable>sourcetype</replaceable> AS <replaceable>targettype</replaceable>) WITHOUT FUNCTION [ AS ASSIGNMENT | AS IMPLICIT ] + +CREATE CAST (<replaceable>sourcetype</replaceable> AS <replaceable>targettype</replaceable>) + WITH INOUT + [ AS ASSIGNMENT | AS IMPLICIT ] </synopsis> </refsynopsisdiv> @@ -59,6 +63,13 @@ SELECT CAST(42 AS float8); </para> <para> + You can define a cast as an <firstterm>I/O conversion cast</> using + the <literal>WITH INOUT</literal> syntax. An I/O conversion cast is + performed by invoking the output function of the source data type, and + passing the result to the input function of the target data type. + </para> + + <para> By default, a cast can be invoked only by an explicit cast request, that is an explicit <literal>CAST(<replaceable>x</> AS <replaceable>typename</>)</literal> or @@ -200,6 +211,18 @@ SELECT CAST ( 2 AS numeric ) + 4.0; </varlistentry> <varlistentry> + <term><literal>WITH INOUT</literal></term> + + <listitem> + <para> + Indicates that the cast is an I/O conversion cast, performed by + invoking the output function of the source data type, and passing the + result to the input function of the target data type. + </para> + </listitem> + </varlistentry> + + <varlistentry> <term><literal>AS ASSIGNMENT</literal></term> <listitem> @@ -284,15 +307,12 @@ SELECT CAST ( 2 AS numeric ) + 4.0; It is normally not necessary to create casts between user-defined types and the standard string types (<type>text</>, <type>varchar</>, and <type>char(<replaceable>n</>)</type>, as well as user-defined types that - are defined to be in the string category). <productname>PostgreSQL</> will - automatically handle a cast to a string type by invoking the other - type's output function, or conversely handle a cast from a string type - by invoking the other type's input function. These - automatically-provided casts are known as <firstterm>I/O conversion - casts</>. I/O conversion casts to string types are treated as - assignment casts, while I/O conversion casts from string types are + are defined to be in the string category). <productname>PostgreSQL</> + provides automatic I/O conversion casts for that. The automatic casts to + string types are treated as assignment casts, while the automatic casts + from string types are explicit-only. You can override this behavior by declaring your own - cast to replace an I/O conversion cast, but usually the only reason to + cast to replace an automatic cast, but usually the only reason to do so is if you want the conversion to be more easily invokable than the standard assignment-only or explicit-only setting. Another possible reason is that you want the conversion to behave differently from the |