编辑代码

CREATE DATABASE test;
use test;
CREATE TABLE homo (
	SX int,
	SNAME varchar(255)
);
CREATE TABLE SC (
	SX int,
	CX int
);
CREATE TABLE C (
	CX int,
	n varchar(255)
	
);
INSERT INTO homo VALUES (1, '手动');
INSERT INTO homo VALUES (2, '法国');
INSERT INTO homo VALUES (3, '是到付');
INSERT INTO homo VALUES (4, '十大');
INSERT INTO homo VALUES (5, '撒大苏打');
INSERT INTO homo VALUES (6, '大师大卫');

INSERT INTO SC VALUES (1, 1);
INSERT INTO SC VALUES (2, 2);
INSERT INTO SC VALUES (3, 1);
INSERT INTO SC VALUES (4, 3);
INSERT INTO SC VALUES (5, 2);
INSERT INTO SC VALUES (6, 2);

INSERT INTO C VALUES (1, 'MATHS');
INSERT INTO C VALUES (2, 'PE');
INSERT INTO C VALUES (3, 'EE');

SELECT SX,SNAME FROM homo 
WHERE SX IN
(
    SELECT SX FROM SC
    WHERE CX IN
    (
        SELECT CX FROM C
        WHERE n='MATHS'
    )
)