Column constraints - DEFAULT and CHECK

CREATE TABLE teachers (
                        id INTEGER,
                        name TEXT,
                        age INTEGER,
                        contact TEXT
                      );
INSERT INTO teachers VALUES
                        (1, 'Heisenburg', 32, '98712341234'),
                        (2, 'Hannibal', -28, '98634214324'),
                        (3, 'Rutherford', 35, '98556431234');

CREATE TABLE teachers (
                        id INTEGER,
                        name TEXT NOT NULL,
                        age INTEGER CHECK (age > 21),
                        contact TEXT
                      );

CREATE TABLE teachers (
                        id INTEGER,
                        name TEXT NOT NULL,
                        age INTEGER CHECK (age > 21),
                        contact TEXT
                      );
INSERT INTO teachers VALUES (1, 'Heisenburg', 32, '98712341234');
INSERT INTO teachers VALUES (2, 'Hannibal', -28, '98634214324');

CREATE TABLE teachers (
                        id INTEGER,
                        name TEXT NOT NULL,
                        age INTEGER CHECK (age > 21),
                        contact TEXT CHECK (LENGTH(contact) = 11)
                      );
INSERT INTO teachers VALUES (1, 'Heisenburg', 32, '98712341234');
INSERT INTO teachers VALUES (2, 'Hannibal', 28, '986342143');