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ballabhoks
Starting Member
18 Posts |
 Posted - 2004-03-08 : 06:47:03
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| What are the major differences between Primary Key and Unique Key |
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Frank Kalis
Constraint Violating Yak Guru
413 Posts |
Posted - 2004-03-08 : 06:51:40
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| A Primary Key Constraint implies that NO value can be NULL, while with a Unique Constraint one value can be NULL. You can only have one PK in a table, but you can have multiple Unique constraints.--Frankhttp://www.insidesql.de |
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nr
SQLTeam MVY
12543 Posts |
Posted - 2004-03-08 : 08:31:05
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| Also a PK is held as a constraint on the table with a unique index to support it.A unique key could just be an index with no corresponding table constraint.More importantly a PK is meant to be a row identifier whereas a unique index just constrains the values. i.e. changing a PK field makes it a different row and so should be implemented as a delete and insert.==========================================Cursors are useful if you don't know sql.DTS can be used in a similar way.Beer is not cold and it isn't fizzy. |
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Difference between PK and UK