A.域完整性約束 B.實(shí)體完整性約束 C.引用完整性約束 D.固有約束
在CREATE TABLE student ( SNO CHAR(7) NOT NULL, SNAME VARCHAR(8) NOT NULL, SEX CHAR(2) NOT NULL, BDATE DATE NOT NULL, HEIGHT DEC(3,2) DEFAULT 0.00, PRIMARY KEY(SNO), CHECK (HEIGHT>0) );中, PRIMARY KEY(SNO) 是()