CHECK

The CHECK constraint allows you to specify a condition that must be satisfied for the data in a column. This constraint is used to enforce domain integrity by limiting the values that can be inserted into a column. For example, consider a table employees with a column salary that should be greater than or equal to 0. The CHECK constraint can be applied as follows:

CREATE TABLE employees (
    employee_id INT PRIMARY KEY,
    first_name VARCHAR(50),
    last_name VARCHAR(50),
    salary DECIMAL(10, 2) CHECK (salary >= 0)
);

In this case, the CHECK constraint ensures that the salary column in the employees table contains only values greater than or equal to 0.

name	type
employee_id	INT
first_name	VARCHAR(50)
last_name	VARCHAR(50)
salary	DECIMAL(10, 2)

In the table above, the salary column in the employees table is constrained by the CHECK constraint to have values greater than or equal to 0.