SQL constraints are used to specify rules for the data in a table. Constraints are used to limit the type of data that can go into a table. This ensures the accuracy and reliability of the data in the table. If there is any violation between the constraint and the data action, the action is aborted. Constraints can be column level or table level.

In SQL, we can add rules for a column while inserting new values in a table. In this tutorial, you will learn about constraints in SQL with the help of examples.

Jan 30, 2025 · By enforcing specific rules on table columns, SQL constraints help maintain data consistency, preventing invalid data entries and optimizing query performance. In this article, we will explain the most common SQL constraints in detail, providing clear examples and explaining how to implement them effectively.

Oct 11, 2022 · There are five different types of SQL constraints. They are: Primary Key Constraint: this ensures all rows have a unique value and cannot be NULL, often used as an identifier of a table’s row. Foreign Key Constraint: this ensures that values in a column (or several columns) match values in another table’s column/s.

May 9, 2023 · SQL Server supports six types of constraints for maintaining data integrity. They are as follows. FOREIGN KEY constraint. Note: Constraints are imposed on columns of a table. Before going to understand the constraints in SQL Server, first, we need to understand NULL in SQL Server. NULL represents the absence of data or value.

Feb 21, 2025 · SQL Constraints are used to specify the rules for the data in a table. These are used to limit which type of data must be stored in the database, and aims to increase the accuracy and reliability of the data stored in the database.

Apr 9, 2024 · SQL Constraints are the rules defined on tables and columns in SQL Server to maintain data correctness and consistency of data stored in database. Constraints are parameters that are used while creating table to define column validation to accepts the values in column. and maintain accurate data.

Constraints in SQL can include NOT NULL, UNIQUE, PRIMARY KEY, and FOREIGN KEY. Other helpful parameters are CHECK DEFAULT and CREATE INDEX, which help maintain accuracy when accessing or retrieving information in a database.

SQL constraints are rules enforced on data columns in SQL Server databases. They ensure the accuracy and reliability of the data in the database. By restricting the type of data that can be stored in a particular column, constraints prevent invalid data entry, which is crucial for maintaining the overall quality of the database.

SQL constraints define rules for the data in a database to maintain accuracy, consistency, and integrity. They ensure that only valid data is stored, preventing issues like duplicate entries, missing values, or invalid relationships. SQL constraints are applied at the column or table level when creating or modifying a table.