[SQL] Too many rows returning

[Linh Luong]

Hi,

Does the number of rows affect how long it takes to execute a query.

I have 3 UNIONS.
One table has 97 rows, another has 7375 rows, and 1558;
In each union there are at least one LEFT OUTER JOIN and each subselect
has at least 2 JOINed tables.

Something like this:
        select ..,..,,...,.
        from 
        (subselect. ...
          ) as T1
         LEFT JOIN
        (subselect ...
         ) as T2
        on T1.field1=T2.field2

        UNION

        select ..,..,,...,.
        from 
        ((subselect. ...) as T1 LEFT JOIN
        (subselect ....) as T2 on T1.field1=T2.field1) as T3
         LEFT JOIN
        (subselect ...
         ) as T2
        on T1.field1=T2.field2

        UNION

        select ..,..,,...,.
        from 
        (subselect. ...
          ) as T1
         LEFT JOIN
        (subselect ...
         ) as T2
        on T1.field1=T2.field2
        


When I do my sql stmt it takes more than 10minutes to return and
sometimes it display the maximum 30 sec has exceed...

Can anyone provide any suggestion in how I can speed up the execution
and possibly return something to me without the error message.

I have tried index but it doesn't seem to have an affect.. because I did
the explain it still using seq scan.. (re: last post "using indexes")

Thanks again


Linh

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