更新columnA或ColumnB或ColumnC时触发触发器

Question

我有代码只在更新单个特定列时触发触发器.触发器用于触发一个函数,该函数将引发一个postgres"notify"事件,我正在监听它,并且需要测试并验证新输入的详细信息.account_details表上有许多值可以更改,不需要帐户验证,因此仅在AFTER UPDATE(没有时间)的触发器是不好的.

    CREATE TRIGGER trigger_update_account_details
    AFTER UPDATE ON account_details
    FOR EACH ROW
    WHEN (OLD.email IS DISTINCT FROM NEW.email) 
    EXECUTE PROCEDURE notify_insert_account_details();

但是,如果许多列中的一个发生变化,我想触发触发器

WHEN (OLD.email IS DISTINCT FROM NEW.email OR 
OLD.username IS DISTINCT FROM NEW.username OR 
OLD.password IS DISTINCT FROM NEW.password) 

但OR不是触发器的有效关键字.试图搜索要使用的关键字而不是OR似乎没有提出任何由于单词OR的性质:-(

Answer 1

这是一种误解.WHEN触发器定义boolean的子句需要一个表达式,您可以OR在其中使用运算符.这应该工作(假设所有列实际存在于表中account_details).我自己使用类似的触发器:

CREATE TRIGGER trigger_update_account_details
AFTER UPDATE ON account_details
FOR EACH ROW
WHEN (OLD.email    IS DISTINCT FROM NEW.email
   OR OLD.username IS DISTINCT FROM NEW.username
   OR OLD.password IS DISTINCT FROM NEW.password) 
EXECUTE PROCEDURE notify_insert_account_details();

评估表达式的成本很低,但这可能比替代方案更可靠:

CREATE TRIGGER ... AFTER UPDATE OF email, username, password ...

因为,根据文件:

当列的UPDATE OFcolumn_name 任何列在UPDATE命令SET列表中列为目标时,将触发特定于列的触发器(使用语法定义的触发器) .即使未触发触发器,列的值也可能会更改,因为BEFORE UPDATE不会考虑通过触发器对行的内容所做的更改.相反,UPDATE ... SET x = x ...即使列的值没有改变,诸如的命令也会在列x上触发触发器.

ROW 检查许多列的类型语法较短(做同样的事情):

CREATE TRIGGER trigger_update_account_details
AFTER UPDATE ON account_details
FOR EACH ROW
WHEN ((OLD.email, OLD.username, OLD.password, ...)
       IS DISTINCT FROM
      (NEW.email, NEW.username, NEW.password, ...))
EXECUTE PROCEDURE notify_insert_account_details();

或者,检查行中的每个可见用户列:

...
WHEN (OLD IS DISTINCT FROM NEW)
...

Answer 2

我认为你不需要这个WHEN条款.您可以在UPDATE子句中指定有问题的列:

CREATE TRIGGER trigger_update_account_details
    AFTER UPDATE OF email, username, password ON account_details
    FOR EACH ROW
    EXECUTE PROCEDURE notify_insert_account_details();