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Query to find nth max salary in table EMP

 
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anshul_gugnani

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PostPosted: Fri Feb 12, 2010 2:14 pm    Post subject: Query to find nth max salary in table EMP
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Hi,

Can Anyone please explain me the logic behind the below query to find the nth max salary in EMP table -

Quote:
select sal from emp A where n =

( select count(*) from emp B where A.sal < B.sal )





Thanks
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enrico-sorichetti

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PostPosted: Fri Feb 12, 2010 2:16 pm    Post subject: Reply to: Query to find nth max salary in table EMP
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topic moved where it belongs!
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dick scherrer

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PostPosted: Fri Feb 12, 2010 2:28 pm    Post subject:
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Hello,

Suggest you write down 5 "salaries" and manually step thru the process.

This will quickly show what happens when the query processes.
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anshul_gugnani

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PostPosted: Fri Feb 12, 2010 3:21 pm    Post subject:
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Hi
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dick scherrer

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PostPosted: Fri Feb 12, 2010 10:38 pm    Post subject: Reply to: Query to find nth max salary in table EMP
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Quote:
Hi
Well, it is a start. . . icon_confused.gif
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anshul_gugnani

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PostPosted: Fri Feb 12, 2010 11:15 pm    Post subject:
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Hi, Say I have 5 salaries as -

12, 25, 13, 78, 03

According to
Quote:
select count(*) from emp B where A.sal < B.sal


each salary will have a count for which it is greater then other salaries in table.

So result for records will be this will be -

3, 1, 3, 0, 4

Now, According to
Quote:
select sal from emp A where (n-1) =



25 is salary whose count is equal to (n-1).

Please suggest if my understanding is correct. I think this co-related subquery.

Thanks!
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dick scherrer

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PostPosted: Sat Feb 13, 2010 3:01 am    Post subject:
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Hello,

Other than the typo (3, 1, 3, 0, 4) , i believe you have it correctly icon_smile.gif

Also - Fromthe db2 manual (i added the bold for emphasis):
Quote:
A subquery is actually executed for each row of R only if it includes a correlated reference. In fact, a subquery with no correlated references is executed just once, whereas a subquery with a correlated reference may have to be executed once for each row.
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anshul_gugnani

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PostPosted: Sat Feb 13, 2010 3:15 pm    Post subject:
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Hi,

Quote:
Other than the typo (3, 1, 3, 0, 4) ,


Could you please explain as to why this is wrong??

Thanks
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dick scherrer

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PostPosted: Sat Feb 13, 2010 3:57 pm    Post subject:
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Hello,

Maybe 3, 1, 2, 0, 4 . . .?
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