使用mysql中另一個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從tbltransfer值改變location的價值在哪裏tblequipments在eq_id是tblequipments等於在tbltransfer的eq_id。這是我想出的查詢：

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將在update語句中爲每行運行子查詢。這是更好地利用加入這裏：

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