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What's the difference between a primary key and a unique key?
3 Answers
Primary Doesn't allow any dublicate value and null value.
But unique allow only one null value.
simple and easy
Ramprit SahaniPosted Jan 30, 2015, 5:06 AM
Hi,
You can have multiple unique keys in a table but can have only one Primary Key.
Primary key and unique key does not allow enter duplicate data.Primary key doesn't allow null value.Unique key allows only one null value.
PradeepPosted Aug 18, 2009, 1:24 AM
Both primary key and unique enforce uniqueness of the column on which
they are defined. But by default primary key creates a clustered index
on the column, where are unique creates a nonclustered index by
default. Another major difference is that, primary key doesn't allow
NULLs, but unique key allows one NULL only.
they are defined. But by default primary key creates a clustered index
on the column, where are unique creates a nonclustered index by
default. Another major difference is that, primary key doesn't allow
NULLs, but unique key allows one NULL only.
Purushottam RathorePosted Jul 29, 2009, 6:41 AM