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Re: Problem with LEF OUTER JOIN
Posted by: wdeveloper
Date: March 20, 2006 04:04AM

Hi

I have currently made no indexes on the table and all is default. I am not a very advanced user of SQL.

The basic point of speed is that when I remove the clause V.UserID=1 then a cross join is made between all the records of the table, where as we need to just compare a few of them by filtering it with the clause.

As I also explained before that its not just the V.UserID=1 would always fetch no records, rather it fetches no record is there is no satisfying records in tblthreadvisitsbyuser table. This I had read as null-rejected, where is there is no matching record in second table the query is optimized as an outer join. For more info on this refer:
http://dev.mysql.com/doc/refman/5.0/en/outer-join-simplification.html
http://dev.mysql.com/doc/refman/5.0/en/left-join-optimization.html

Thanks
Sandy

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