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Optimizing my SQL Query - which is better?

Posted on 2016-09-14
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Last Modified: 2016-09-14
I have two ways of doing this query, and would like the experts advice on which is better in terms of performance.

One where statement that says
 pe.PAT_ID NOT IN
  (SELECT PAT_ID FROM Patient_type WHERE PATIENT_TYPE_C IN  (1,2))

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or
pt.PATIENT_TYPE_C not in  (1,2)

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--where I have to add the table connections in the FROM clause of the main query
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Question by:Becky Edwards
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7 Comments
 
LVL 46

Expert Comment

by:Vitor Montalvão
ID: 41797828
No doubt at all for the 2nd option.
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Expert Comment

by:ste5an
ID: 41797844
Sorry, but this question makes no senses, cause both options refer to different table alias names.

Please post a concise and complete example. In your case the entire queries.
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LVL 46

Expert Comment

by:Vitor Montalvão
ID: 41797853
My understanding is if she should have a JOIN between Patient and Patient_type or if she should use the NOT IN clause.
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Author Comment

by:Becky Edwards
ID: 41797878
Thank you Vitor for clarifying.
   Some coworkers said I should not use the Not In Clause, which enables me to filter out certain patients without pulling in the table PATIENT_TYPE into the main query itself.  

So instead of doing this in the where clause:
PAT_ENC.PAT_ID NOT IN
  (SELECT PAT_ID FROM Patient_type WHERE PATIENT_TYPE_C IN  (1,2))

Open in new window


I would do this:
IN THE FROM CLAUSE
Add left outer join PATIENT_TYPE            pt ON PAT_ENC.PAT_ID=pt.PAT_ID
and this:
IN THE WHERE CLAUSE
pt.PATIENT_TYPE_C not in  (1,2)
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Author Comment

by:Becky Edwards
ID: 41797882
Also Viktor:
Can you tell me why someone would use the first option?  I copied it from someone else's query.
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Accepted Solution

by:
Vitor Montalvão earned 500 total points
ID: 41797902
I think you don't need the LEFT OUTER JOIN since you're filtering by PATIENT_TYPE_C. An INNER JOIN should be better here.

Can you tell me why someone would use the first option?
Because you're not getting the benefit of the relationship between the two tables (PK and FK that you'll use in the JOIN clause).
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Author Closing Comment

by:Becky Edwards
ID: 41797916
Thank you Vitor for your assistance.  I will make changes accordingly.  Have a great day!
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What is SQL Server and how does it work?

The purpose of this paper is to provide you background on SQL Server. It’s your self-study guide for learning fundamentals. It includes both the history of SQL and its technical basics. Concepts and definitions will form the solid foundation of your future DBA expertise.

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