How to check if trigger exists in PostgreSQL?

Question

I want to verify correctness of database migrations which add triggers to some tables. I'm using sqitch , so I'd like to find a way to check it with SQL queries. I believe it should be possible with postgres system tables, but I currently can't find a way to do this.

Answer 1

Use the catalog pg_trigger .

A simple lookup for a table books :

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

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

Using pg_proc to get the source of the trigger function:

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)

Example of the pg_get_triggerdef() function usage:

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) 

In a Sqitch verify script you can use an anonymous code block, eg:

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

Answer 2

to check by trigger name you can do it:

select trigger_name from information_schema.triggers 
WHERE trigger_name = 'your_trigger_name'

Also can select with other information.

select event_object_schema as table_schema,
       event_object_table as table_name,
       trigger_schema,
       trigger_name,
       string_agg(event_manipulation, ',') as event,
       action_timing as activation,
       action_condition as condition,
       action_statement as definition
from information_schema.triggers
group by 1,2,3,4,6,7,8
order by table_schema,
         table_name;

Column details

• table_schema - name of the table schema
• table_name - name of the trigger table
• trigger_schema - name of the trigger schema
• trigger_name - name of the trigger
• event - specific SQL operation: Insert, Update or Delete
• activation - trigger activation time: After, Instead of or BEFORE
• condition - trigger activation condition
• definition - definition of trigger - in postgreSQL it is always EXECUTE PROCEDURE function_name()

If you don't want to select event_manipulation , you may remove the group by in the query.

reference