MySQL UNIQUE Constraint Tutorial

Create a Table with UNIQUE Constraints

Create a MySQL table named 'employees' with columns 'id', 'email', and 'phone'. Add UNIQUE constraints on 'email' and 'phone'.

Expected output: A table 'employees' with UNIQUE constraints on email and phone columns.

Hint: Use UNIQUE keyword in CREATE TABLE statement for email and phone columns.

Insert Data and Test UNIQUE Constraint

Insert multiple rows into the 'employees' table and try inserting duplicate emails or phone numbers to observe constraint enforcement.

Expected output: Duplicate inserts should fail with a UNIQUE constraint violation error.

Hint: Use INSERT statements and observe errors on duplicates.

A PRIMARY KEY uniquely identifies each row and cannot contain NULLs, while a UNIQUE constraint enforces uniqueness but allows one NULL value per column.

Yes, a table can have multiple UNIQUE constraints on different columns or combinations of columns.

MySQL allows one NULL value per UNIQUE column because NULL is not considered equal to any other NULL.