postgresql如何在没有任何变化的情况下停止触发添加行

Question

我想将对我的working 表的更改记录到我的history 表中，但前提是值在UPDATE 期间发生了更改，我尝试创建一个update_history 触发器，但它无论值是否已更改，都会添加一行，例如，假设我的工作表中有这个:

shift_id|site     |organisational_unit
--------|---------|-------------------
  123475|site01   |my org              

如果我执行更新查询

UPDATE working SET site = $1, organisational_unit = $2 WHERE shift_id=$3', ['site01', 'my new org', '123475']

这会在历史表中为 site 创建一行，甚至认为它没有改变值我只想为 organisational_unit 更改创建一个新行

historyid|shiftid|fieldname          |oldvalue |newvalue   |updatedat          |
---------|-------|-------------------|---------|-----------|-------------------|
        7| 123475|organisational_unit|my org   |my new org |2019-07-01 10:21:19|
        8| 123475|site               |site01   |site01     |2019-07-01 10:21:19|

我的触发器看起来像这样

-- create function for updates to track history
CREATE function update_history ()
RETURNS TRIGGER
as $$
BEGIN
    -- check if data in column has changed between the update
    IF NEW.client_id <> OLD.client_id THEN

        -- if it has insert a row to the history table detailing the changes
        INSERT INTO history (ShiftId, fieldName, OldValue, NewValue)
        VALUES(New.shift_id, 'client id ', OLD.client_id, NEW.client_id);

    -- if nothing has changed don't do anything
    END IF;

    IF NEW.organisational_unit <> OLD.organisational_unit THEN
        INSERT INTO history (ShiftId, fieldName, OldValue, NewValue)
        VALUES(New.shift_id, 'organisational_unit', OLD.organisational_unit, NEW.organisational_unit);
    END IF;

    IF NEW.site <> OLD.site THEN
    INSERT INTO history
        (ShiftId, fieldName, OldValue, NewValue)
    VALUES(New.shift_id, 'site', OLD.site, NEW.site);
    END IF;

return null;
END;
$$
language plpgsql;

Answer 1

最有效的方法是定义一个仅在某些列更改时触发的触发器:

CREATE TRIGGER ... BEFORE UPDATE ON ... FOR EACH ROW
   WHEN (NEW IS DISTINCT FROM OLD)
   EXECUTE FUNCTION update_history();

这避免了在不必要的情况下执行函数。