CHECK with Boolean Expression
CHECK with Boolean Expression is a SQL statement in the Constraints category. CHECK constraints validate data against boolean expressions. Can use IN, BETWEEN, LIKE, comparisons, etc. The syntax is CONSTRAINT name CHECK (column IN ('value1', 'value2')). It returns cHECK constraint. A typical example: CREATE TABLE products ( id INT PRIMARY KEY, name VARCHAR(100), price DECIMAL(10,2), quantity INT, category VARCHAR(20), CONSTRAINT ck_price_positive CHECK (price >= 0), CONSTRAINT ck_quantity_non_negative CHECK (quantity >= 0), CONSTRAINT ck_valid_category CHECK (category IN ('Electronics', 'Clothing', 'Food')), CONSTRAINT ck_name_not_empty CHECK (LENGTH(TRIM(name)) > 0) ); -- Multiple CHECK constraints ensure data quality -- CHECK constraints are evaluated for each row on INSERT/UPDATE A close relative is PRIMARY KEY, which a column or set of columns that uniquely identifies each row. Only one PK per table. Automatically creates a unique index. A close relative is FOREIGN KEY, which ensures referential integrity: values in this column must exist in the referenced parent table.