<!-- $Header: /cvsroot/pgsql/doc/src/sgml/ref/create_cast.sgml,v 1.5 2002/09/18 21:35:20 tgl Exp $ -->

<!-- $Header: /cvsroot/pgsql/doc/src/sgml/ref/create_cast.sgml,v 1.6 2002/10/04 22:08:44 tgl Exp $ -->

<refentry id="SQL-CREATECAST">

<refmeta>

</programlisting>

will be allowed only if the cast from type <type>timestamp</> to

<type>text</type> is marked <literal>AS IMPLICIT</>. Otherwise it

will be necessary to writeone of

will be necessary to writethe cast explicitly, for example

<programlisting>

SELECT 'The time is ' || CAST(now() AS text);

SELECT 'The time is ' || now()::text;

</programlisting>

(We generally use the term <firstterm>implicit

cast</firstterm> to describe this kind of cast.)

<para>

To be able to create a cast, you must own the source or the target

data type.

data type. To create a binary-compatible cast, you must be superuser

(this restriction is made because an erroneous binary-compatible cast

conversion can easily crash the server).

</para>

<variablelist>

}

{

int16typ1len;

int16typ2len;

booltyp1byval;

booltyp2byval;

chartyp1align;

chartyp2align;

funcid=InvalidOid;

if (!superuser())

elog(ERROR,"Must be superuser to create a cast WITHOUT FUNCTION");

get_typlenbyvalalign(sourcetypeid,&typ1len,&typ1byval,&typ1align);

get_typlenbyvalalign(targettypeid,&typ2len,&typ2byval,&typ2align);

if (typ1len!=typ2len||

typ1align!=typ2align)

elog(ERROR,"source and target datatypes are not physically compatible");

}