如何检查PostgreSQL中是否存在触发器？

Question

我想验证将触发器添加到某些表的数据库迁移的正确性。我正在使用sqitch，因此我想找到一种使用SQL查询进行检查的方法。我相信postgres系统表应该有可能，但是我目前找不到实现此目的的方法。

Answer 1

使用目录pg_trigger。

一个简单的表查询books：

select tgname
from pg_trigger
where not tgisinternal
and tgrelid = 'books'::regclass;

    tgname     
---------------
 books_trigger
(1 row)

使用pg_proc得到触发功能的来源：

select tgname, proname, prosrc 
from pg_trigger
join pg_proc p on p.oid = tgfoid
where not tgisinternal
and tgrelid = 'books'::regclass;

    tgname     |    proname    |                    prosrc
---------------+---------------+------------------------------------------------
 books_trigger | books_trigger |                                               +
               |               | begin                                         +
               |               |     if tg_op = 'UPDATE' then                  +
               |               |         if new.listorder > old.listorder then +
               |               |             update books                      +
               |               |             set listorder = listorder- 1      +
               |               |             where listorder <= new.listorder  +
               |               |             and listorder > old.listorder     +
               |               |             and id <> new.id;                 +
               |               |         else                                  +
               |               |             update books                      +
               |               |             set listorder = listorder+ 1      +
               |               |             where listorder >= new.listorder  +
               |               |             and listorder < old.listorder     +
               |               |             and id <> new.id;                 +
               |               |             end if;                           +
               |               |     else                                      +
               |               |         update books                          +
               |               |         set listorder = listorder+ 1          +
               |               |         where listorder >= new.listorder      +
               |               |         and id <> new.id;                     +
               |               |     end if;                                   +
               |               |     return new;                               +
               |               | end
(1 row)

pg_get_triggerdef()函数用法示例：

select pg_get_triggerdef(t.oid) as "trigger declaration"
from pg_trigger t
where not tgisinternal
and tgrelid = 'books'::regclass;

                                             trigger declaration                
--------------------------------------------------------------------------------------------------------------
 CREATE TRIGGER books_trigger BEFORE INSERT OR UPDATE ON books FOR EACH ROW EXECUTE PROCEDURE books_trigger()
(1 row)

在Sqitchverify脚本中，您可以使用匿名代码块，例如：

do $$
begin
    perform tgname
    from pg_trigger
    where not tgisinternal
    and tgrelid = 'books'::regclass;
    if not found then 
        raise exception 'trigger not found';
    end if;
end $$;