SQL Server

engine runs these validations on the column values before it inserts or updates them. Hence helping in maintaining the integrity, accuracy & reliability of the data

The check constraint in SQL Server allows us to validate data values that are being inserted or updated in one or more columns. If the validation fails, then SQL Server will not insert or update the data.

Unique Constraint or Unique key in SQL Server enforces the uniqueness of the column value. i.e. no two rows of a table can have the same values. In this tutorial, we will learn how to create a Unique Constraint, how to drop it, how to add a Unique key to an existing table, etc.

Foreign key in SQL Server is used to establish the relationship between tables. In this tutorial, we will learn what is Foreign Key ?. How to create a Foreign Key constraint. How to add it to an existing table. Learn how to Drop the it etc.

A primary key in SQL Server is a field (or combination of fields) in the table that uniquely identifies each row or record. In this tutorial let us learn what is a Primary key. We will learn how to create a Primary Key constraint. Learn to add or drop the Primary key from an existing table. We also look at how to change the primary key index from clustered to non clustered and also change the sort order from ascending to descending etc.