Update Select批量更新

CREATE TABLE dualx(       x_id VARCHAR(5) NOT NULL ,       x_con VARCHAR(10))CREATE TABLE dualy(       y_id VARCHAR(5) NOT NULL ,       y_con VARCHAR(10))INSERT INTO dualx VALUES ('1','xxx');INSERT INTO dualx VALUES ('2','xxx');INSERT INTO dualx VALUES ('3','xxx');INSERT INTO dualy VALUES ('1','111');INSERT INTO dualy VALUES ('2','222');INSERT INTO dualy VALUES ('3','333');UPDATE dualx   SET (x_con) = (SELECT y.y_con  FROM  dualy y WHERE dualx.x_id = y.y_id)SELECT * FROM dualx;SELECT * FROM dualy;DROP TABLE dualx;DROP TABLE dualy;

UPDATE dualx SET (x_con) = (SELECT y.y_con FROM dualy y WHERE dualx.x_id = y.y_id) 其中SELECT y.y_con FROM dualy y WHERE dualx.x_id = y.y_id不能返回多行，否则报错。