What slows down that query?

From: Gad Krosner <krosner_at_excite.com>
Date: Sat, 21 Oct 2000 00:55:09 GMT
Message-ID: <8sqphc$5vr$1@nnrp1.deja.com>

Hi There!

I'm new to Oracle, so please bear with me...

I wrote a query like this:
Select <col list >
From a, b, c

WHERE a.pk = b.fk1
  and c.pk = b.fk2
  and a.col1 = 'Y'

  and substr (a.col2, 1, 3) = 'abc'

The query runs fine - brings results back in a few seconds. Then, I added another condition,
  and a.col3 = 1
This condition brings the server to its knees - I waited more than 3 minutes for the rows to come back. And it wasn't a fluke - I kept commenting this newly added condition, to speed up the query and vice versa. col3 is numeric, with three possible values, 1, 2 or 3.

Any explanation for this?
Any way to debug or analyze the server's interpretation?

Thanks.

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Before you buy. Received on Fri Oct 20 2000 - 19:55:09 CDT