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What is a unique key in SQL ?
Unique Key is a constraint in SQL. So, before understanding what exactly is a primary key, let’s understand what exactly is a constraint in SQL. Constraints are the rules enforced on data columns on a table. These are used to limit the type of data that can go into a table. Constraints can either be column level or table level.
Unique Key:
Whenever we give the constraint of unique key to a column, this would mean that the column cannot have any duplicate values present in it. In other words, all the records which are present in this column have to be unique
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