更新MySQL表字段，只有当条件满足

Question

我有这个疑问：

UPDATE orders SET tracking = '$trackingnumber', tracking_timestamp = NOW() 
WHERE comment like '%$ordernumber%' 

是否有可能更新tracking_timestamp仅当字段的值0000-00-00 00:00:00？

Answer 1

您可以使用CASE

UPDATE orders 
SET tracking = '$trackingnumber', 
tracking_timestamp = CASE 
WHEN tracking_timestamp='0000-00-00 00:00:00' 
THEN NOW() 
ELSE tracking_timestamp 
END 
WHERE comment like '%$ordernumber%' 

Answer 2

使用此查询

UPDATE orders 
SET tracking = '$trackingnumber', 
tracking_timestamp = IF (tracking_timestamp='0000-00-00 00:00:00',NOW(),'0000-00-00 00:00:00') 
WHERE COMMENT LIKE '%$ordernumber%'