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sql query SQL 2005

Posted on 2010-11-29
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HI,

I have a repor to fix and somebody has used this:

SELECT cast (case count(1) when 0 then 1 else 0 end as bit) ColumnA From TableX

totally intrigued why?

ColumnA returns either 0 or 1. Why count(1) is used and why 0 or 1?

Thanks
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Question by:shmz
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7 Comments
 
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Expert Comment

by:hackpin
ID: 34235501
well it the query uses count to check if there are records in table, you can use count(field name).
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LVL 14

Expert Comment

by:Christopher Gordon
ID: 34235538
heh, I agree strange syntax.  You usually see count(*) used to represent what the author is accomplishing with that query.  

All that is doing is counting the number of records in the result set.  You could really replace that with 0, or 1, or 2, or 'Eat at Joes' for that matter.

Count(*) is how i'd of wrote it instead of count(1).
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Author Comment

by:shmz
ID: 34235570
well, it seems that it turn to be 'true' or false when I run it in SQL server 2005 Report.

And then inside the report it checks to display a table in the report based on this value:

IIF (First(ColumnA.Value), "dataset1"), False, True)

I don't understand why if the result is 0 then 1 else 0....
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Christopher Gordon earned 2000 total points
ID: 34235593
SELECT cast (case count(1) when 0 then 1 else 0 end as bit) ColumnA From TableX

If TableX has data then return 0 (i.e when number of rows is 0 hen return true)

If TableX has no data return 1 (i.e. when number of rows is not 0 (then return false)



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LVL 1

Expert Comment

by:_DJ
ID: 34236556
count(1) Will return number of records selected from TableX.
CASE WHEN works as if else so if count(1) is 0 then it will return 1 else 0
and cast will convert it in true and false
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LVL 7

Expert Comment

by:rmm2001
ID: 34241649
Rewrite it..

SELECT cast (case count(*) when 0 then 1 else 0 end as bit) ColumnA From TableX

So SELECT COUNT(*) FROM Table. If COUNT(*) = 0 then return true (a 1). If its <> 0 then return false (a 0)

If the first value in ColumnA = "dataset1" then report back false. Else it's true.
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Author Closing Comment

by:shmz
ID: 34253947
Thanks
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