编辑代码

CREATE DATABASE test;
use test;
CREATE TABLE S
(
SNO VARCHAR(6) PRIMARY KEY ,
SN VARCHAR(10) NOT NULL ,
SD VARCHAR(16),
SB DATE,
SEX VARCHAR(2) DEFAULT '男',
CHECK (SEX IN ('男', '女')) 
); 

CREATE TABLE C
(
CNO VARCHAR(6) PRIMARY KEY,
CN VARCHAR(10),
PC VARCHAR(6),
FOREIGN KEY (PC) REFERENCES C(CNO)
);

CREATE TABLE SC
( SNO VARCHAR(6),
 CNO VARCHAR(6),
 GRADE DEC(4,1),
 PRIMARY KEY (SNO, CNO),  
 FOREIGN KEY (SNO) REFERENCES S(SNO),
 FOREIGN KEY (CNO) REFERENCES C(CNO),
 CHECK (GRADE BETWEEN 0 AND 100)
);
 
CREATE INDEX I_sSN ON S(SN);
CREATE INDEX I_sSdSn ON S(SD DESC,SN);

CREATE TABLE SC 
(
    SNo CHAR (6) NOT NULL,
    CNo CHAR (4) NOT NULL,
    GRADE tintint NULL,
    PRIMARY KEY(SNo,CNo),
    INDEX(GRADE)
)