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what is difference between "Primary key" and "Unique key"?
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Answer Posted / swapna
1)unique key can be null but primariy key cant be null.
2)primariy key can be refrenced to other table as FK.
Primary key and unique are Entity integrity constraints
Primary key allows each row in a table to be uniquely
identified and ensures that no duplicate rows
exist and no null values are entered.
Unique key constraint is used to prevent the duplication of
key values within the rows of a table and allow null
values. (In oracle, one null is not equal to another null).
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