出现错误的最可能解释

"There is no OLD row in on INSERT trigger"

是您正在执行创建 AFTER INSERT 触发器的语句，而不是创建 AFTER UPDATE 触发器.

is that you are executing a statement that's creating an AFTER INSERT trigger, rather than creating an AFTER UPDATE trigger.

不能从行中引用 OLD 值的原因是该行在 INSERT 之前存在，是因为该行在 INSERT 之前不存在.

The reason that you can't reference OLD values from the row, as the row existed prior to the INSERT, is that the row did not exist prior to the INSERT.