I wonder if it would be beneficial to add an additional where clause which
can prefilter the data so you only need to perform the full calculation on a
subset of records.
I haven't done the math, but let's supposed that point_x is 10 and that for
any result of your long calculation to be true, then x must be between 5 and
15, then you can use the where clause
WHERE
X BETWEEN 5 AND 15
AND (point_x - x)^2 + (point_y -y)^2 < R^2;
If you can make this type of pre-calculation and get a proper range for X
then it can reduce the number of records that need to be checked. I'm
assuming SQLite will use an index on X for BETWEEN (I don't know for sure).
Also you should do testing to be sure this query really is faster in
practice--I'm only theorizing here. :-)
HTH,
Sam
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-----Original Message-----
From: bash [mailto:[EMAIL PROTECTED]
Sent: Wednesday, May 09, 2007 10:33 AM
To: sqlite-users@sqlite.org
Subject: Re: [sqlite] perfomance degradation for expr "foo = X or bar =X"
On Wed, 9 May 2007 18:13:07 +0400
Tomash Brechko <[EMAIL PROTECTED]> wrote:
Im currently thinking about this table:
CREATE TABLE map (
x int,
y int,
name char
);
CREATE INDEX map_x ON map(x);
CREATE INDEX map_y ON map(y);
And query for it will be something like this (circle):
SELECT name
FROM map
WHERE (point_x - x)^2 + (point_y -y)^2 < R^2;
How SQLite will works? Is there any benefit in indexes?
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