CHECK constraint in SQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a CHECK constraint in SQL?

A CHECK constraint is a rule that limits the values allowed in a column. It ensures data meets specific conditions before being saved.

beginner

How does a CHECK constraint help maintain data quality?

It prevents invalid data by allowing only values that satisfy the condition defined in the CHECK constraint.

beginner

Write a simple CHECK constraint to ensure age is 18 or older.

CHECK (age >= 18)

intermediate

Can a CHECK constraint use multiple conditions? Give an example.

Yes, using AND or OR. Example: CHECK (age >= 18 AND age <= 65) ensures age is between 18 and 65.

beginner

What happens if you try to insert data that violates a CHECK constraint?

The database rejects the insert or update and shows an error, preventing invalid data from being saved.

What does a CHECK constraint do in a database?

A Creates a backup of the database

B Limits values in a column based on a condition

C Deletes duplicate rows automatically

D Encrypts data in a column

A CHECK constraint limits the values allowed in a column by enforcing a condition.

Which of the following is a valid CHECK constraint for a salary column to be positive?

A CHECK (salary > 0)

B CHECK salary > 0

C CHECK salary = positive

D CHECK (salary IS NOT NULL)

The correct syntax uses parentheses and a condition: CHECK (salary > 0).

Can a CHECK constraint use logical operators like AND or OR?

A Only AND is allowed, not OR

B No, only one condition is allowed

C Only OR is allowed, not AND

D Yes, to combine multiple conditions

CHECK constraints can combine multiple conditions using AND or OR.

What happens if data violates a CHECK constraint during insertion?

A The database automatically fixes the data

B The data is inserted anyway

C The insertion fails with an error

D The data is inserted but marked invalid

The database rejects the insert and shows an error to maintain data integrity.

Which SQL keyword is used to add a CHECK constraint when creating a table?

A CHECK

B LIMIT

C CONDITION

D RESTRICT

The CHECK keyword defines the condition for the constraint.

Explain what a CHECK constraint is and how it helps keep data correct.

Think about rules that data must follow before saving.

Write an example of a CHECK constraint that ensures a product price is greater than zero and less than 1000.

Use AND to combine two conditions inside CHECK.