MySQL — Check

Basic CHECK Constraint

CREATE TABLE products (
    id INT PRIMARY KEY,
    name VARCHAR(100),
    price DECIMAL(10,2) CHECK (price > 0),
    quantity INT CHECK (quantity >= 0)
);

Named CHECK

CREATE TABLE employees (
    id INT PRIMARY KEY,
    age INT,
    salary DECIMAL(10,2),
    CONSTRAINT chk_age CHECK (age >= 18 AND age <= 65),
    CONSTRAINT chk_salary CHECK (salary > 0)
);

CHECK with Multiple Columns

CREATE TABLE bookings (
    start_date DATE,
    end_date DATE,
    CHECK (end_date > start_date)
);

Adding CHECK After Creation

ALTER TABLE products ADD CONSTRAINT chk_price CHECK (price > 0);

Dropping CHECK

ALTER TABLE products DROP CHECK chk_price;

CHECK Examples

Condition	Use Case
CHECK (price > 0)	Positive prices only
CHECK (email LIKE '%@%')	Email format
CHECK (length(code) = 5)	Fixed length
CHECK (status IN ('A','B','C'))	Limited values

Mini Practice

Write SQL code that:

1. Creates a table with CHECK constraints
2. Adds a CHECK with a named constraint
3. Creates a multi-column CHECK
4. Tests the CHECK with valid and invalid data

Up Next

Continue with Default — providing automatic values.