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Minor copy-editing.

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Tom Lane 2002-09-01 02:37:02 +00:00
parent 681ed4e2fe
commit 1903221517
1 changed files with 9 additions and 8 deletions
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doc/src/sgml/ref/create_cast.sgml
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@ -1,4 +1,4 @@
<!-- $Header: /cvsroot/pgsql/doc/src/sgml/ref/create_cast.sgml,v 1.2 2002/08/11 17:44:12 petere Exp $ --> <!-- $Header: /cvsroot/pgsql/doc/src/sgml/ref/create_cast.sgml,v 1.3 2002/09/01 02:37:02 tgl Exp $ -->
<refentry id="SQL-CREATECAST"> <refentry id="SQL-CREATECAST">
<refmeta> <refmeta>
@ -28,8 +28,8 @@ CREATE CAST (<replaceable>sourcetype</replaceable> AS <replaceable>targettype</r
<para> <para>
<command>CREATE CAST</command> defines a new cast. A cast <command>CREATE CAST</command> defines a new cast. A cast
specifies which function can be invoked when a conversion between specifies how to perform a conversion between
two data types is requested. For example, two data types. For example,
<programlisting> <programlisting>
SELECT CAST(42 AS text); SELECT CAST(42 AS text);
</programlisting> </programlisting>
@ -49,7 +49,7 @@ SELECT CAST(42 AS text);
</para> </para>
<para> <para>
A cast can marked <literal>AS ASSIGNMENT</>, which means that it A cast can be marked <literal>AS ASSIGNMENT</>, which means that it
can be invoked implicitly in any context where the conversion it can be invoked implicitly in any context where the conversion it
defines is required. Cast functions not so marked can be invoked defines is required. Cast functions not so marked can be invoked
only by explicit <literal>CAST</>, only by explicit <literal>CAST</>,
@ -72,7 +72,7 @@ INSERT INTO foo(f1) VALUES(42);
<productname>PostgreSQL</productname> to choose surprising <productname>PostgreSQL</productname> to choose surprising
interpretations of commands, or to be unable to resolve commands at interpretations of commands, or to be unable to resolve commands at
all because there are multiple possible interpretations. A good all because there are multiple possible interpretations. A good
rule of thumb is to make cast implicitly invokable only for rule of thumb is to make a cast implicitly invokable only for
information-preserving transformations between types in the same information-preserving transformations between types in the same
general type category. For example, <type>int2</type> to general type category. For example, <type>int2</type> to
<type>int4</type> casts can reasonably be implicit, but be wary of <type>int4</type> casts can reasonably be implicit, but be wary of
@ -161,9 +161,10 @@ INSERT INTO foo(f1) VALUES(42);
<para> <para>
Prior to PostgreSQL 7.3, every function that had the same name as a Prior to PostgreSQL 7.3, every function that had the same name as a
data type, returned that data type, and took one argument of a data type, returned that data type, and took one argument of a
different type was automatically a cast function. This system has different type was automatically a cast function. This convention has
been abandoned in face of the introduction of schemas and to be been abandoned in face of the introduction of schemas and to be
able to store binary compatible casts. The built-in cast functions able to represent binary compatible casts in the catalogs. The built-in
cast functions
still follow this naming scheme, but they have to be declared as still follow this naming scheme, but they have to be declared as
casts explicitly now. casts explicitly now.
</para> </para>
@ -175,7 +176,7 @@ INSERT INTO foo(f1) VALUES(42);
<para> <para>
To create a cast from type <type>text</type> to type To create a cast from type <type>text</type> to type
<type>int</type> using the function <literal>int4(text)</literal>: <type>int4</type> using the function <literal>int4(text)</literal>:
<programlisting> <programlisting>
CREATE CAST (text AS int4) WITH FUNCTION int4(text); CREATE CAST (text AS int4) WITH FUNCTION int4(text);
</programlisting> </programlisting>