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Re: NULLS and string concatenation

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Don Drake <dondrake(at)gmail(dot)com>
Cc: Richard Huxton <dev(at)archonet(dot)com>, pgsql-sql(at)postgresql(dot)org
Subject: Re: NULLS and string concatenation
Date: 2004-11-19 20:01:42
Message-ID: 13631.1100894502@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-sql
Don Drake <dondrake(at)gmail(dot)com> writes:
> This is still strange to me.  In Oracle, the same query would not
> replace the *entire* string with a NULL, it treats the NULL as a no
> value.

Oracle is a bit, um, standards-challenged.  They fail to make a
distinction between an empty string and a NULL, but such a distinction
is both logically necessary and required by the SQL standard.

> I can't find in the documentation where string concatenation of any
> string and NULL is NULL.

SQL92 section 6.13 <string value expression>, General Rule 2a:

            a) If either S1 or S2 is the null value, then the result of the
              <concatenation> is the null value.

			regards, tom lane

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