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Unique Index on duplicate value column

 
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simimathew

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Joined: 26 Jan 2006
Posts: 23
Location: London

PostPosted: 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

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Joined: 13 Feb 2004
Posts: 551
Location: Bangalore

PostPosted: 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

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PostPosted: 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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