update from select

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。