In this post, I will explain What is Unique Key?
Unique Key provides uniqueness for a column or set of columns in a table like a primary key. It is used to prevent duplicate values in a column. A database table can have more than one Unique Key and it allows at least one NULL value in a column( Nullable). Unique Key generates a Unique Non-Clustered Index
Example of Unique Key-
Create a Unique Key while creating a table
CREATE TABLE tbl_Employee
(
EmpId INT NOT NULL,
EmpName VARCHAR(100) NULL,
CONSTRAINT UC_EmpId UNIQUE (EmpId)
)
Create Unique Key using alter table statement
ALTER TABLE tbl_Employee
ADD CONSTRAINT UC_EmpId UNIQUE (EmpId)
Drop Unique Key using alter table statement
ALTER TABLE tbl_Employee
DROP CONSTRAINT UC_EmpId