In line sub query versus join query

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In line sub query versus join query

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amsqlguy
Yak Posting Veteran

89 Posts

Posted - 2010-10-27 : 09:26:17

Guys,

I am trying to figure out the advantages and disadvantages in terms of performance for in line sub query versus join based query.

In the below query the EMPLOYEE_TYP and EMPLOYEE_STATUS table have only 10 rows each whereas EMPLOYEE and EMPLOYEE_DEM have 17mill rows each.

Inline Query

SELECT E.FIRST_NAME, E.LAST_NAME, E.DISPLAYNAME, D.SSN, D.DOB, (SELECT EMP_TYP_CD FROM EMPLOYEE_TYP T WHERE T.EMP_TYP_ID = E.EMP_TYP_ID) as EMP_TYP_CD,
(SELECT EMP_STATUS_CD FROM EMPLOYEE_STATUS S WHERE S.EMP_STATUS_ID = E.EMP_STATUS_ID) AS EMP_STATUS_CD
FROM EMEPLOYEE E INNER JOIN EMPLOYEE_DEM D
ON E.ID = D.EMPID
---- OUTPUT 17MILL ROWS

Join Query

SELECT E.FIRST_NAME, E.LAST_NAME, E.DISPLAYNAME, D.SSN, D.DOB, T.EMP_TYP_CD, S.EMP_STATUS_CD
FROM EMEPLOYEE E INNER JOIN EMPLOYEE_DEM D
ON E.ID = D.EMPID
INNER JOIN EMPLOYEE_TYP T ON E.EMP_TYP_ID = T.EMP_TYP_ID
INNER JOIN EMPLOYEE_STATUS S ON E,EMP_STATUS_ID = T.EMP_STATUS_ID
---- OUTPUT 17MILL ROWS

Any suggestions or inputs would help

Thanks

webfred
Master Smack Fu Yak Hacker

8781 Posts

Posted - 2010-10-27 : 09:36:02

SQL Server should be able to analyze and optimize that kind of statements in most cases.
Have a look at both execution plans to see what happens.

No, you're never too old to Yak'n'Roll if you're too young to die.

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