CHECK

CREATE TABLE Persons (
    Id INTEGER NOT NULL,
    LastName VARCHAR(255) NOT NULL,
    FirstName VARCHAR(255),
    Age INTEGER,
    City VARCHAR(255),
    CONSTRAINT CK_Person_Age CHECK (Age >= 18)
);

ALTER TABLE Persons
ADD CONSTRAINT CK_Person_Age CHECK (Age >= 18);

ALTER TABLE Persons
DROP CHECK CK_Person_Age;