Unique key constraint uniquely identifies each record in the database. This key provides uniqueness for the column or set of columns.
The Unique key cannot accept a duplicate value.
The unique key can accept only on Null value.
A unique key in SQL is a set of one or more columns in a table that uniquely identifies each record in that table. It ensures that the values in the specified columns are unique across all the rows in the table.
The primary purpose of a unique key is to enforce the integrity of the data by preventing duplicate or null values in the specified columns. It is often used to identify individual records in a table and is a crucial concept in database design.
In SQL, a unique key can be defined using the UNIQUE constraint when creating or altering a table. The unique key can be composed of one or more columns, and it guarantees that the combination of values in those columns will be unique for each row in the table.