NOT NULL制約 チェック制約 一意性制約(UNIQUE KEY) 主キー制約 (PRIMARY KEY) 参照整合性制約、外部キー制約 (FOREIGN KEY) NOT NULL NULL値を禁止 CREATE TABLE product ( product_id INT PRIMARY KEY , product_name VARCHAR(16) UNIQUE NOT NULL , price INT ) ; CREATE TABLE user ( user_id INT PRIMARY KEY , age INT , city_code CHAR(4) , gender CHAR(1), CONSTRAINT agecity_check CHECK(age >= 18 OR city_code = '0003'), CONSTRAINT gendercheck CHECK(ge