使用mysql中另一个表的值更新表中的值

Question

我有tbltransfer其中包含location和eq_id。我想用location从tbltransfer值改变location的价值在哪里tblequipments在eq_id是tblequipments等于在tbltransfer的eq_id。这是我想出的查询：

UPDATE tblequipments 
    SET LocationName = (
     SELECT t.Location from tbltransfer as t 
     join tblequipments as e on t.eq_ID = e.eq_ID 
     WHERE t.transactionID=%s 
    ) 

Answer 1

mysql将在update语句中为每行运行子查询。这是更好地利用加入这里：

UPDATE 
    tblequipments, 
    tbltransfer 
SET 
    tblequipments.location = tbltransfer.location 
WHERE 
    tblequipments.eq_id = tbltransfer.eq_id 
AND 
    tbltransfer.transactionID = %s 

Answer 2

UPDATE tblequipments 
INNER JOIN tbltransfer ON tblequipments.eq_ID = tbltransfer.eq_ID 
SET tblequipments.LocationName=tbltransfer.Location 
WHERE tbltransfer.transactionID=%s