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Re: CAST and timestamp

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: mike(at)thegodshalls(dot)com
Cc: KeithW(at)narrowpathinc(dot)com,PostgreSQL Novice <pgsql-novice(at)postgresql(dot)org>
Subject: Re: CAST and timestamp
Date: 2004-12-21 04:14:37
Message-ID: 2488.1103602477@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-novice
Mike G <mike(at)thegodshalls(dot)com> writes:
> If you want to go from char / varchar to numeric or date types then you
> need to cast them as text first and then the final data type.

BTW, to enlarge on this a bit:

The conversion functions that are actually supplied in pg_cast go from
text to float4 or timestamp.  In many situations Postgres will
automatically use these same functions for conversions from varchar or
char, because it knows that the latter datatypes are just about the same
as text.  However, in a scenario where you explicitly specify a cast,
the system will insist on finding an exact match to the requested type
conversion in pg_cast --- this is so that you can be sure that you get
exactly the coercion you asked for, and not some surprising variant.

If you want, you can add entries to the pg_cast catalog to allow direct
coercions from varchar in all the same places where text can be
converted.  I'd not recommend treating char the same, since it's really
not quite the same thing (trailing blank suppression and all that).
See CREATE CAST ...

			regards, tom lane

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