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simimathew
Joined: 26 Jan 2006
Posts: 17
Location: London
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| Posted: Tue Jul 08, 2008 9:26 pm Post subject: Unique Index on duplicate value column |
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Hi,
1) Can a unique index be created on a column that already has duplicate values? I tried doing it on DB2 UDB and it is not letting me create a unique index.
2) But I remember having read somewhere that two nulls are considered to be equal for UNIQUE indexing purposes. How do you create a UNIQUE INDEX on an already existing nullable column?
3) Also could you please point out the difference between primary key and unique index?
Many Thanks,
Simi |
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ashimer
Joined: 13 Feb 2004
Posts: 313
Location: Bangalore
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| Posted: Wed Jul 09, 2008 3:02 pm Post subject: |
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Quote:
somewhere that two nulls are considered to be equal
Only a single null value is allowed in an UNIQUE indexing column ...
Primary key will not allow any NULL ...
Unique itself means no duplicates are allowed ... |
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simimathew
Joined: 26 Jan 2006
Posts: 17
Location: London
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| Posted: Wed Jul 09, 2008 3:18 pm Post subject: Reply to: Unique Index on duplicate value column |
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| Thanks very much. |
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