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Order of WHERE statements in Sybase SQL Server

betsywr
betsywr asked
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Last Modified: 2010-04-15
I'm working on tuning some SQL in a Sybase DB and have found a number of queries which don't seem to be utilizing the indexes efficiently on the DB tables.  It seems to me that in a join statement, the most logical order for the WHERE statments would be an order which first checks fields that are indexed on each table.  For example:

SELECT a.column1,
       b.column2
FROM   table1 a,
       table2 b
WHERE  a.indexed_column1 = :hstvariable1
AND    a.indexed_column2 = :hstvariable2
AND    b.indexed_column1 = a.indexed_column1
AND    b.unindexed_column1 = :hstvariable3

(I hope that this is making sense.)  In other words, can reordering the WHERE conditions help performance by eliminating some reads on the tables?
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Commented:
Whoops...I didn't mean to enter this under the C topic.  Sorry for any confusion!
In a simple query like this, I would think that the query optimiser would already be taking this information into account.

When it comes to designing a RDBMS engine, the SQL parser/optimiser is given a lot of attention. If you think about it, one of the primary functions of the engine is to process SQL.

Commented:
Reording can optimise your query.
The best result you get when using sub-queries.

Author

Commented:
How can I find out the order that the optimiser is using?

Author

Commented:
How can I find out the order that the optimiser is using?
Commented:
This one is on us!
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