SQL Constraints: Managing Data Integrity Effectively

Create a Table with Multiple Constraints

Design and create a SQL table named 'Products' with columns for ProductID (primary key), ProductName (not null), Price (check price > 0), and CategoryID (foreign key).

Expected output: A Products table with correctly defined constraints enforcing data integrity.

Hint: Use CREATE TABLE with appropriate constraints and name them explicitly.

Modify an Existing Constraint

Add a CHECK constraint to the Employees table to ensure the LastName column has at least 3 characters.

Expected output: A new CHECK constraint on LastName enforcing minimum length.

Hint: Use ALTER TABLE ADD CONSTRAINT with a suitable CHECK condition.

Drop a Constraint

Remove the CHECK constraint on the FirstName column from the Employees table.

Expected output: The specified CHECK constraint is removed from the table.

Hint: Use ALTER TABLE DROP CONSTRAINT with the constraint's name.

A PRIMARY KEY uniquely identifies each row and does not allow NULLs, while a UNIQUE constraint ensures all values are distinct but can allow one NULL in some databases.

FOREIGN KEY constraints enforce referential integrity by ensuring that values in a child table correspond to existing values in a parent table.

Most SQL databases require dropping the existing constraint before adding a modified version, as direct modification is often not supported.