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Super key explanation

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mistryvipulh
Starting Member

4 Posts

Posted - 2010-08-01 : 08:38:15

Hello frnds

Can anybody explain me the following topic in simple english language

1. Primary Key
2. Unique key
3. Super Key
4. Candidate Key
5. Composite Key
and a difference between Unique key, super key, candidate key and composite key

Thanks in advance
Regards
Vipul

harrisunderwork
Starting Member

4 Posts

Posted - 2010-08-02 : 01:01:15

SK - Any combination of keys that make it unique.
Ck - Minimum SK is called candidate key.
PK - Any CK which does not take null value.
FK - Reference to PK of another table with no nulls
UK - Same feature is PK but can take null values. Also, in a table there can be many UK.

I hope this helps.

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