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Message Posted: Tue, 04 Jan 2011 @ 07:36:16 GMT


     
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Subj:   Re: Need help on LEFT JOIN - count more than left
 
From:   Minakshi Swami

Hi,

This is simply because your id (the joining column) in first table have more than one recs in second table.

For eg.

First table has below values

     emp_id   name
     1        a

Second table have below values

     emp_id   name
     1        b
     1        c
     1        ?
     1        b

Now the result of below query will 4, because for each matching value it will count the corresponding row in second table

     sel count(*) from
     first a
     left join
     second b
     on a.emp_id=b.emp_id

Incase you join on emp_id and name both then the count(*) will give 1(values for corresponding row of second table will null).If you give where (b.emp_id is not null and b.name is not null) then left join will work as inner join.


Regards

Meenakshi



     
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