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Regarding query efficiency

 
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sathish_rathinam

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Joined: 22 Aug 2005
Posts: 59
Location: india

PostPosted: Wed Jul 30, 2008 11:46 am    Post subject: Regarding query efficiency
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Hi ,

I want to know which one of the two queries written below is performance efficient

1.SELECT DISTINCT A . CUST_ID_NUMBER

FROM TEJAPCL_AP_CT_LK A

WHERE A . CUST_ID_NUMBER NOT IN (

SELECT A . CUST_ID_NUMBER

FROM TEJAPCL_AP_CT_LK A , TEJAPTM_AP_TR_MSTR B

WHERE B . APP_REF_NUMBER = A . APP_REF_NUMBER GROUP BY

CUST_ID_NUMBER )




2.SELECT DISTINCT C . CUST_ID_NUMBER

FROM TEJAPCL_AP_CT_LK C

WHERE NOT EXISTS (

SELECT A . CUST_ID_NUMBER

FROM TEJAPCL_AP_CT_LK A , TEJAPTM_AP_TR_MSTR B

WHERE B . APP_REF_NUMBER = A . APP_REF_NUMBER

AND C.CUST_ID_NUMBER = A.CUST_ID_NUMBER )



Regards,
Sathish
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dbzTHEdinosauer

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Joined: 20 Oct 2006
Posts: 6966
Location: porcelain throne

PostPosted: Wed Jul 30, 2008 12:48 pm    Post subject:
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since you obviously ran an explain, what did the explain indicate?
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ashimer

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Joined: 13 Feb 2004
Posts: 551
Location: Bangalore

PostPosted: Wed Jul 30, 2008 2:14 pm    Post subject:
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Quote:


since you obviously ran an explain, what did the explain indicate?



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sudhakar84

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Joined: 20 Jun 2008
Posts: 21
Location: chennai

PostPosted: Wed Jul 30, 2008 4:45 pm    Post subject: Reply to: Regarding query efficiency
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Hi,

If the result of the outer query is small and the result set of the inner sub-query is large, then use EXISTS - if it is the other way around, then use the IN clause.
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