Primary Key : A primary key is a constaints on a column which enforce uniqly identifies records in the table in the database.
- A primary key must be unique and can not be NULL.
- A table can have only primary key.
To create primary key on new table
CREATE TABLE myTable
EmpId int NOT NULL PRIMARY KEY,
FirstName varchar(50) NOT NULL,
To create primary on an existing table need to do following
ALTER TABLE myTable ADD PRIMARY KEY (EmpId)