By: Simon (yea and verily - for tis me)

Simon (yea and verily - for tis me) — Tue, 22 Jun 2010 09:47:25 +0000

In that far off theme park called Teradataland (the rides are big, but a bit dull), we’re always taught that NULL effectively has no meaning – it cannot be equated to (or, by derivation, specifically not equated to), so NULL = NULL is false, NULL NULL is also false as is = NULL etc. etc. – it can only be tested using IS NULL and IS NOT NULL. There are a few functions like ZeroIfNULL and COALESCE that deal with it as well, similarly to NVL.

All the above examples have identical outcomes on Teradata, incidentally, except the NVL one, as that doesn’t exist as a keyword on T12.

However, the most efficient method I’ve found to do what you’re last query is doing (on Teradata) is:
SELECT b.bloke_name
FROM
beauty b
LEFT JOIN
truth t
ON t.bloke_name = b.bloke_name
WHERE t.bloke_name IS NULL
;

Don’t let the DBAs tell you otherwise – this works when other methods don’t (on huge tables when properly indexed) and is significantly faster.

I tried to work in ‘RIGHT JOIN Claude’, but it got too contrived – sorry, that’s an in-joke that shouldn’t go on blogs, I guess.

Gotta do some real work now – day off tomorrow vuvuzela-ing for Engerland.

Cheers

Si M…

Comments on: Gullible about Nullable – Stuff I thought I knew…and didn’t

By: Simon (yea and verily - for tis me)