rdelaage/postgresql
1
0
Fork 0
mirror of https://git.postgresql.org/git/postgresql.git synced 2024-10-01 14:01:23 +02:00
Code Issues Packages Projects Releases Wiki Activity

Minor copy-editing.

Browse Source
This commit is contained in:
Tom Lane 2002-09-01 02:37:02 +00:00
parent 681ed4e2fe
commit 1903221517
1 changed files with 9 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

17
doc/src/sgml/ref/create_cast.sgml
View File

@ -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">
<refmeta>
@ -28,8 +28,8 @@ CREATE CAST (<replaceable>sourcetype</replaceable> AS <replaceable>targettype</r
<para>
<command>CREATE CAST</command> defines a new cast. A cast
specifies which function can be invoked when a conversion between
two data types is requested. For example,
specifies how to perform a conversion between
two data types. For example,
<programlisting>
SELECT CAST(42 AS text);
</programlisting>
@ -49,7 +49,7 @@ SELECT CAST(42 AS text);
</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
defines is required. Cast functions not so marked can be invoked
only by explicit <literal>CAST</>,
@ -72,7 +72,7 @@ INSERT INTO foo(f1) VALUES(42);
<productname>PostgreSQL</productname> to choose surprising
interpretations of commands, or to be unable to resolve commands at
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
general type category. For example, <type>int2</type> to
<type>int4</type> casts can reasonably be implicit, but be wary of
@ -161,9 +161,10 @@ INSERT INTO foo(f1) VALUES(42);
<para>
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
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
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
casts explicitly now.
</para>
@ -175,7 +176,7 @@ INSERT INTO foo(f1) VALUES(42);
<para>
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>
CREATE CAST (text AS int4) WITH FUNCTION int4(text);
</programlisting>