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simimathew
New User
Joined: 26 Jan 2006
Posts: 23
Location: London
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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
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| Quote: |
somewhere that two nulls are considered to be equal
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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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Joined: 26 Jan 2006
Posts: 23
Location: London
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| Thanks very much. |
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