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Re: comparing rows

From: Don Baccus <dhogaza(at)pacifier(dot)com>
To: Thomas Lockhart <lockhart(at)alumni(dot)caltech(dot)edu>, Magnus Hagander <mha(at)sollentuna(dot)net>
Cc: "'Tom Lane'" <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Tatsuo Ishii <t-ishii(at)sra(dot)co(dot)jp>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: comparing rows
Date: 2000-08-03 13:52:53
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-hackers
At 01:44 PM 8/3/00 +0000, Thomas Lockhart wrote:
>> Not compatible with the current release of MS SQL/MSDE :-) At least not
>> fully.
>The original issue was that "foo = NULL" is *not* a legal SQL92

Ummm...I think this is wrong, and I have Date on my side (I just
checked).  foo = NULL is NULL, just like foo + NULL is NULL.

If foo = NULL is illegal, doesn't this make it rather difficult to
say things like table1.i = table2.i for tables that contain NULLs
in column i?

Oracle allows it, and returns NULL.  Oracle's fairly trustworthy
on low-level standards compliance over things like NULL (not
entirely, though - it treats '' as NULL in the VALUES list of
an INSERT, though not elsewhere, for instance).

NULL = NULL is also perfectly legal, returning NULL.  Before one
gets too excited, NULL <> NULL and NULL < NULL etc all return
NULL, too, along with NULL = <anything> so it's not terribly
useful, which is why IS NULL exists.

- Don Baccus, Portland OR <dhogaza(at)pacifier(dot)com>
  Nature photos, on-line guides, Pacific Northwest
  Rare Bird Alert Service and other goodies at

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