What Is The Difference Between Unique And Primary Key Constraints?

1.	What Is The Difference Between Unique And Primary Key Constraints?
Answer» There should be only one PRIMARY KEY in a table WHEREAS there can be any number of UNIQUE Keys. PRIMARY KEY doesn’t ALLOW NULL VALUES whereas Unique key allows NULL values. There should be only one PRIMARY KEY in a table whereas there can be any number of UNIQUE Keys. PRIMARY KEY doesn’t allow NULL values whereas Unique key allows NULL values.

Answer»

There should be only one PRIMARY KEY in a table WHEREAS there can be any number of UNIQUE Keys.

PRIMARY KEY doesn’t ALLOW NULL VALUES whereas Unique key allows NULL values.

There should be only one PRIMARY KEY in a table whereas there can be any number of UNIQUE Keys.

PRIMARY KEY doesn’t allow NULL values whereas Unique key allows NULL values.

Discussion