A primary key in SQL Table helps to identify each row/record in a table uniquely.
Here is the characteristic of Primary Key in SQL Table
- Primary keys must contain unique values
- primary key column cannot have NULL values
- Table can have only one primary key (can be composite with multiple fields)
How to create Primary key in SQL
ColumnName datatype not null identity(1,1) PRIMARY KEY
, Note: identity(1,1) seed not Necessary while creating the primary key, but in general we set the identity seed for Primary Key column most of the time.
CREATE TABLE ClassStudentMap (
CSId int not null identity(1,1) PRIMARY KEY,
ClassId int NOT NULL,
StudentId bigint NOT NULL
You may check the Foreign Key
to understand the more insight about Primary Key.