有没有办法只处理更新前MySQL触发器中更改的记录？
我需要一个语句，允许在更新表 2 时更改表 1 中的某些字段。
我目前有以下代码：
delimiter //
CREATE TRIGGER check BEFORE UPDATE ON table2
FOR EACH ROW
BEGIN
IF NEW.Count <> OLD.Count THEN
...
END IF;
END//
delimiter ;
但是，table1非常大并且有很多更新事件，所以我担心这段代码会减慢我的服务器速度。所以我想知道是否有某种解决方案不会查看其中的所有记录，而只查看更新的记录？
I need a statement that allows to change some fields in table1 when table2 was updated.
I have currently the following code:
delimiter //
CREATE TRIGGER check BEFORE UPDATE ON table2
FOR EACH ROW
BEGIN
IF NEW.Count <> OLD.Count THEN
...
END IF;
END//
delimiter ;
However, table1 is very large and there are a lot of update events, so I'm afraid that this code can slowdown my server. So I want to know if there is some solution that will not look over all records in it, but only those updated?
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触发器不会“查看”所有记录。因为您将触发器声明为
FOR EACH ROW，所以触发器中只会处理单行。当触发器针对每一行执行时，
NEW和OLD引用单行，这意味着条件NEW.Count <> OLD.Count只是比较两个（简单）列值The trigger will not "look" over all records. Because you declared the trigger as
FOR EACH ROWonly a single row will be dealt with in the trigger.As the trigger is execute for each row,
NEWandOLDreference a single row as, which means that the conditionNEW.Count <> OLD.Countsimply compares two (simple) column values