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How to get a union query to return distinct rows

Posted on 2011-02-15
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Last Modified: 2012-06-27
Hi

Is there a way to get a union query to only return a distinct set of rows if there is overlap in the rows returned by the multiple select statements?

thanks
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Question by:andieje
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Guy Hengel [angelIII / a3] earned 2000 total points
ID: 34900286
UNION does already a distinct, implicitly (unlike UNION ALL which does not perform a distinct).

however, UNION and DISTINCT both do the distinct on the returned column sets, not just on a "primary key" field.

so, you need to clarify what exactly you consider "distinct", and apply some sql techniques accordingly.
consider reading this article to find explanations and solution: http://www.experts-exchange.com/A_3203.html
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Author Closing Comment

by:andieje
ID: 34900469
thanks
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LVL 61

Expert Comment

by:HainKurt
ID: 34900487
check these

(select 1 union select 2)
1
2

(select 1 union select 3 union select 1 union select 2)
1
2
3

(select 1 union select 2)
union
(select 1 union select 3 union select 1 union select 2)
1
2
3
0

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