MySQL 触发“列更新”语法
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MySQL trigger 'update on column' syntax
提问by cldy1020
Can we use a MySQL trigger on update of specific columns, which updates another column in same table (same row)
我们可以在更新特定列时使用 MySQL 触发器，它更新同一表（同一行）中的另一列
create trigger my_trigger
BEFORE UPDATE OF col1, col2 ON TABLE_NAME
for each row
set NEW.col3 = NEW.col3 +1;
I tried the above code using UPDATE OF col1, col2. It is not working in MySQL. What is the correct syntax, can somebody point me to some examples.
我使用UPDATE OF col1, col2. 它在 MySQL 中不起作用。什么是正确的语法，有人可以指点我一些例子。
回答by eggyal
You can't specify that the trigger is to be run only on the update of specific columns (an UPDATEaffects the entire record), but you can test which columns have been updated within your trigger:
您不能指定触发器仅在更新特定列时运行（UPDATE影响整个记录），但您可以测试哪些列已在您的触发器中更新：
DELIMITER ;;
CREATE TRIGGER my_trigger BEFORE UPDATE ON TABLE_NAME FOR EACH ROW
IF NOT (NEW.col1 <=> OLD.col1 AND NEW.col2 <=> OLD.col2) THEN
SET NEW.col3 = NEW.col3 + 1;
END IF;;
DELIMITER ;
