Union or Union All

Which query should I use if I don't want duplicates:
  Union or Union All
schmir1Asked:
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pssandhuCommented:
Union All
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Aneesh RetnakaranDatabase AdministratorCommented:
Union wont return the duplicates

Union all returns everything
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pssandhuCommented:
Oops... my bad, I though you wanted duplicates
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Guy Hengel [angelIII / a3]Billing EngineerCommented:
> if I don't want duplicates:
it depends on what you define a "duplicate".

union will do a distinct, but only over ALL the columns returned by the query.
if your "duplicates" are in a single (or part of the ) column(s), neither will work, but you will need to change the query eventually completely.
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shru_0409Commented:
The UNION clause forces all rows returned by each portion of the UNION to be sorted and merged and duplicates to be filtered before the first row is returned to the calling module.

A UNION ALL simply returns all rows including duplicates and does not have to perform any sort, merge, or filter.
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awking00Information Technology SpecialistCommented:
Just so you can see the difference, see the attached. Notice how the union results are ordered and the union all results are just stacked.
union-queries.txt
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schmir1Author Commented:
Thanks for all your help.  I think I have a good understanding of Union now.
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Query Syntax

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