Delete from join 用法

CREATE TABLE YSHA 
(
    code VARCHAR(10),
    NAME VARCHAR(20)
)

CREATE TABLE YSHB
( 
   code VARCHAR(10),
   col VARCHAR(10)
)

INSERT INTO YSHA VALUES (1,‘A1‘)
INSERT INTO YSHA VALUES (2,‘A2‘)

INSERT INTO YSHB VALUES(1,‘Row1‘)
INSERT INTO YSHB VALUES(1,‘Row2‘)
INSERT INTO YSHB VALUES(1,‘Row3‘)
INSERT INTO YSHB VALUES(3,‘Row1‘)

DELETE A FROM YSHA A LEFT JOIN YSHB B ON A.code=b.code WHERE b.code is NULL
SELECT * FROM YSHA
SELECT * FROM YSHB

DELETE FROM YSHA WHERE NOT EXISTS(SELECT 1 FROM YSHB B WHERE YSHA.code=b.code )
SELECT * FROM YSHA
SELECT * FROM YSHB