CHECK Constraint

CREATE TABLE User (  
    uid int primary key,  
    firstName text,  
    lastName text NOT NULL,  
    age int CHECK (age > 12 and age < 120),  
    email text,  
    phone text,  
    CHECK (email is not NULL or phone is not NULL)  
)

Similar to FK, but not supported

CREATE TABLE Purchase (
    prodName CHAR(30)
        CHECK (prodName IN (
            SELECT Product.name
            FROM Product
        )),
    date DATETIME NOT NULL
);