What are the most commonly used constraints available in SQL?

The following constraints are commonly used in SQL: NOT NULL – Ensures that a column cannot have a NULL value. CHECK – Ensures that the values in a column satisfies a specific condition. DEFAULT – Sets a default value for a column if no value is specified.

What are 5 types of constraints?

Types of Constraints in DBMS-

• Domain constraint.
• Tuple Uniqueness constraint.
• Key constraint.
• Entity Integrity constraint.
• Referential Integrity constraint.

What are the constraints in SQL Server?

Constraints in SQL Server: SQL NOT NULL, UNIQUE and SQL PRIMARY KEY

• SQL NOT NULL.
• UNIQUE.
• PRIMARY KEY.
• FOREIGN KEY.
• CHECK.
• DEFAULT.

What are the types of constraints in SQL?

Types of SQL Constraints:

• NOT NULL Constraint.
• UNIQUE Constraint.
• DEFAULT Constraint.
• CHECK Constraint.
• PRIMARY KEY Constraint.
• FOREIGN KEY Constraint.

What are the constraints in SQL Server 2017?

October 25, 2017. SQL Server Constraints are predefined rules and restrictions that are enforced in a single column or multiple columns, regarding the values allowed in the columns, to maintain the integrity, accuracy, and reliability of that column’s data.

How are unique constraints referenced in SQL Server?

A UNIQUE constraint can be referenced by a FOREIGN KEY constraint. When a UNIQUE constraint is added to an existing column or columns in the table, by default, the Database Engine examines the existing data in the columns to make sure all values are unique.

When to use a primary key constraint in SQL?

PRIMARY KEY Constraint This constraint is used to identify a particular column or a group of columns that can uniquely identify a row in the table. With the PRIMARY KEY constraint in place, any row cannot have a duplicate value. We cannot have NULL as the value for such a column.

How is the SQL NOT NULL constraint enforced?

In the ID column definition statement, the SQL NOT NULL column-level constraint is enforced, considering the ID column as a mandatory column that should be provided with a valid SQL NOT NULL value. The case is different for the Name column that can be ignored in the INSERT statement, with the ability to provide it with NULL value.