Posted by lelandhuang@gmail.com on 05/18/06 09:37

I am developing reporting service and using lots of 'LEFT OUTER JOIN',
I am worried about the performance and want to use some subquery to
improve
the performance.
Could I do that like below,

[the origin source]
SELECT *
FROM TableA
LEFT OUTER JOIN TableB
ON TableA.item1 = TableB.item1
WHERE TableA.item2 = 'xxxx'
TableB.item2 > yyyy AND TableB.item2 < zzzz

I add the subquery to query every table before 'LEFT JOIN'
--------------------------------------------------------------------------
SELECT *
FROM
(SELECT *
FROM TableA
WHERE TableA.item2 = 'xxxx'
) TableC
LEFT OUTER JOIN
(SELECT *
FROM TableB
WHERE TableB.item2 > yyyy AND TableB.item2 < zzzz
) TableD
ON TableC.item1 = TableD.item1
WHERE TableC.item2 = 'xxxx'
TableD.item2 > yyyy AND TableD.item2 < zzzz
--------------------------------------------------------------------------

Can anyone give me some suggestion?
Thanks a lot.

Leland Huang

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