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Rewriting query for performance

Posted on 2012-03-25
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Last Modified: 2012-07-24
I have a query .
table_1
clientid memberid  denom num
a              x                  1        1
a              y                  1        1
b             z                   0        1

table_2
clientid memberid type
a              x               c
a              y               s
b              z               c

I need to select values where denom=1 and type='c' from the two tables. The denominator value should be sum(denom) where type='c' and denom=1.
denom from table_1 is a flag. I wrote a sub query here. But there are many fields like numerator1,numerator2,etc. So I wrote many subqueries . I dont want to use subqueries here as there is much data. Can anyone suggest me a query which is much efficient than subqueries
select clientid,denominator=(select sum(denom) from table_1 t1
                                      join table_2 t2 on t1.clientid=t2.clientid
                                      where t2.type='C' and denom=1)
from dbo.table_1 t1
join table_2 t2
on t1.clietid=t2.clientid
where t2.type='C'
group by e.lob
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Question by:himabindu_nvn
2 Comments
 
LVL 75

Expert Comment

by:Anthony Perkins
ID: 37763841
Something like this:
SELECT  t1.clientid,
        SUM(t1.denom)
FROM    table_1 t1
        JOIN table_2 t2 ON t1.clientid = t2.clientid
WHERE   t2.type = 'C'
GROUP BY t1.clientid
HAVING  SUM(t1.denom) = 1

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LVL 29

Accepted Solution

by:
Olaf Doschke earned 500 total points
ID: 37764510
It depends what you need, maybe even simpler

SELECT  t1.clientid,
        SUM(t1.denom) as SumDenom, sum(t1.numerator1) as SumNumerator1,...
FROM    table_1 t1
        INNER JOIN table_2 t2 ON t1.clientid = t2.clientid and t2.type='c'
GROUP BY t1.clientid

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I'd recommend you first do a query
SELECT  t1.*
FROM    table_1 t1
        INNER JOIN table_2 t2 ON t1.clientid = t2.clientid and t2.type='c'

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and inspect if you want the sums of this query result. If the join condition differs for each of the sums you want to make, there could still be ways of summing on condition using CASE.

I suspect you also want to add t1.memberid = t2.memberid in your join condition, otherwise you sum same records of t1 multiple times. Not with your sample data, but there might be cases you join records of other members also of type 'c'.

Bye, Olaf.
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