PL / pgSQL：如何使用IF NEW。 <>老。

Question

我是PL / pgSQL编程的新手。我需要在我的表中记录更新列的审计日志

表

create table sample_table(name varchar(15),city varchar(15),age int,mail varchar(20) primary key); 

审计表

create table sample_table__audits_dynamicols(mail varchar(20), columnchanged varchar(10), oldvalue varchar(10), changed_on timestamp(6) NOT NULL)

触发功能

CREATE FUNCTION public.log_sample_table_allchanges() RETURNS trigger AS $BODY$DECLARE
       _colname text;
       _tablename varchar(15) := 'sample_table';
       _schema varchar(15) := 'public';
       _changed_on time := now();
    BEGIN
      FOR _colname IN SELECT column_name FROM information_schema.Columns WHERE table_schema = _schema AND table_name = _tablename LOOP  
         IF NEW._colname <> OLD._colname THEN
            INSERT INTO sample_table__audits_dynamicols(mail,columnchanged, oldvalue ,changed_on)
            VALUES(OLD.mail,_colname,OLD.:_colname,_changed_on);
         END IF;
      END LOOP;
     RETURN NEW;
    END$BODY$
    LANGUAGE plpgsql VOLATILE NOT LEAKPROOF;

触发

create TRIGGER log_sample_table_allchanges
  BEFORE UPDATE
  ON SAMPLE_TABLE
  FOR EACH ROW
  EXECUTE PROCEDURE log_sample_table_allchanges();

要求：每当更改列值时，我都要将其记录为

（邮件，列名，列值，日期）

E.g：

insert into sample_table (name, mail, city, age) values('kanta','[email protected]','hyd',23);
insert into sample_table (name, mail, city, age) values('kmk','[email protected]','hyd',23);

所以当我更新如下

update sample_table set age=24 where mail='[email protected]';
update sample_table set city='bza' where mail='[email protected]'

我想要审计表来记录

([email protected],age,23, timestamp) 
([email protected], city, hyd, timestamp)

现在我在Trigger函数中遇到列比较问题。请帮我纠正我的触发功能以满足我的要求。

Answer 1

您可以使用EXECUTE动态获取列的值并进行比较。

CREATE OR REPLACE FUNCTION public.log_sample_table_allchanges() RETURNS trigger AS 
    $BODY$
      DECLARE
       _colname text;
       _tablename varchar(15) := 'sample_table';
       _schema varchar(15) := 'public';
       _changed_on timestamp := now();
       _old_val text;
       _new_val text;
    BEGIN
      FOR _colname IN SELECT column_name FROM information_schema.Columns WHERE table_schema = _schema AND table_name = _tablename
       LOOP  
          EXECUTE 'SELECT $1.' || _colname || ', $2.' || _colname
           USING OLD,NEW
          INTO _old_val, _new_val; --get the old and new values for the column.

          IF _new_val <> _old_val THEN
            INSERT INTO sample_table__audits_dynamicols(mail,columnchanged, oldvalue ,changed_on)
            VALUES(OLD.mail,_colname,_old_val,_changed_on);
         END IF;
      END LOOP;
     RETURN NEW;
    END$BODY$
    LANGUAGE plpgsql VOLATILE NOT LEAKPROOF;

我不确定为什么你在审计表中将mail定义为PRIMARY KEY，如果同一邮件被更新两次，它将导致unique constraint违规。