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。