The ADD CONSTRAINT command is used to create a constraint after a table is already created. The following SQL adds a constraint named "PK_Person" that is a PRIMARY KEY constraint on multiple …

A foreign key establishes a link between two tables by referencing the primary key of one table as a foreign key in another. To add a foreign key constraint, you use the ALTER TABLE statement with …

Jul 23, 2025 · Prerequisite - SQL Constraints We can create a table with more than one constraint in its columns. Following example shows how we can define different constraints on a table.

Nov 18, 2025 · SQL Server 2022 (16.x) introduces resumable operations for adding table constraints for primary key and unique key constraints. For more information on enabling and using resumable …

Jun 29, 2023 · Learn how to use ADD CONSTRAINT to manage primary keys, foreign keys, and other constraints in SQL databases.

I need to add a constraint to an existing SQL server table but only if it does not already exist. I am creating the constraint using the following SQL. I'm hoping I can add some SQL to the begining of …

Oct 12, 2024 · Learn how to use SQL ALTER TABLE ADD CONSTRAINT to enforce data integrity.

Learn how to add constraints in SQL to enforce data integrity. This guide covers primary, unique, check, and foreign key constraints with examples.

Sep 20, 2025 · Learn how to add a unique constraint to an SQL column using ALTER TABLE. Ensure data integrity and prevent duplicate entries with this step-by-step guide.

We can add constraints using ALTER TABLE Statement followed by ADD CONSTRAINT Command. Most used syntaxes for ADD CONSTRAINTs on existing table are listed as below -