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Primary key constraint in SQL Server Database

SQL PRIMARY KEY Constraint

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.

 
PRIMARY KEY Constraint in SQL Database

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