The CHECK constraint specifies if a value in a column must meet a specific requirement (Boolean expression).
Example: Check Constraint
-- Create Table with CHECK Constraints
CREATE TABLE new_users(
id serial PRIMARY KEY,
first_name VARCHAR(50),
birth_date DATE CHECK(birth_date > '1900-01-01'),
join_date DATE CHECK (join_date > birth_date),
salary integer CHECK(salary > 0)
);## data frame with 0 columns and 0 rows-- Select
SELECT * FROM new_users;## data frame with 0 columns and 0 rows-- INSERT, Should result in an error
INSERT INTO new_users(first_name,birth_date,join_date,salary)
VALUES ('Joe', '1980-02-02', '1990-04-04', -10);## NULL