--- Mike Johnston <[EMAIL PROTECTED]> wrote:
> I have to join three tables to retrieve bits of data from each. I'm wondering
> if I use a view
> are there any performance issues vs. issuing the complete 3 table join query
> in code.
As long as your VIEW/subquery does not make use of
UNION/EXCEPT/INTERSECT, then it's usually the same speed.
I would not recommend complex querying of views/subquery of unions
of selects with large result sets within SQLite. The select will run
much faster and use far less memory if you manually expand these
queries to not make use of the VIEW. SQLite will not perform this
optimization for you.
-- slower
SELECT * FROM (
SELECT a, b FROM t1 WHERE b!=7
UNION ALL
SELECT x, sum(y) FROM t2
WHERE x<9 GROUP BY x HAVING sum(y)>7
) WHERE a>b;
-- faster
SELECT * FROM (
SELECT a, b FROM t1 WHERE b!=7 AND a>b
UNION ALL
SELECT x, sum(y) FROM t2
WHERE x<9 GROUP BY x HAVING sum(y)>7 AND x>sum(y)
);
____________________________________________________________________________________
Bored stiff? Loosen up...
Download and play hundreds of games for free on Yahoo! Games.
http://games.yahoo.com/games/front
-----------------------------------------------------------------------------
To unsubscribe, send email to [EMAIL PROTECTED]
-----------------------------------------------------------------------------
