实体完整性定义(续) (2)在表级定义主码 CREATE TABLE Student (Sno CHAR(9) Sname CHAR(20 NOT NULL, SseX CHAR(2) Sage SMALLINT, Sdept CHAR(20) PRIMARY KEY (Sno) ); An Introduction to Database SystemAn Introduction to Database System 实体完整性定义(续) (2)在表级定义主码 CREATE TABLE Student (Sno CHAR(9)， Sname CHAR(20) NOT NULL， Ssex CHAR(2) ， Sage SMALLINT， Sdept CHAR(20)， PRIMARY KEY (Sno) );