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what is the different between unique+not null & primary key,
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Answer Posted / suresh babu
Unique:
Unique is a constraint,which doesn't allow the duplicate
values and allow only one null value.We can create more
number of unique constraint in single table.
Not Null:
Not Null constraint,which doesn't allow the Null values and
allow the duplicate values.
Primary Key:
We can create one primary key for a table,Which doesn't
allow the duplicate and null values,and used for make a
foreign key relation.we can't do this process using above
two constraints.
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