yes, i agree with Rajesh ,primary key constraint doesn't allow null

What is the difference between UNIQUE CONSTRAINT and
PRIMARY KEY?

1. There is no difference.
2. A PRIMARY KEY cannot be declared on multiple columns.
3. A UNIQUE CONSTRAINT cannot be declared on multiple
columns.
4. A table can have multiple PRIMARY KEYS but only one
UNIQUE CONSTRAINT.
5. A table can have multiple UNIQUE CONSTRAINTs but only
one PRIMARY KEY.

Question Posted / sunitha

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Answer Posted / sunitha

yes, i agree with Rajesh ,primary key constraint doesn't allow null values but unique constraint allows null values.this is the main difference .

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