How to create trigger for all table in postgresql? - database

Question

I have a trigger, but I need to associate with all tables of the my postgres.
Is there a command like this below?
CREATE TRIGGER delete_data_alldb
BEFORE DELETE
ON ALL DATABASE
FOR EACH ROW
EXECUTE PROCEDURE delete_data();

Answer 1

Well there is no database-wide trigger creation but for all such bulk-admin-operations you could use PostgreSQL system tables to generate queries for you instead of writing them by hand.
In this case you could run:
SELECT
'CREATE TRIGGER '
|| tab_name
|| ' BEFORE DELETE ON ALL DATABASE FOR EACH ROW EXECUTE PROCEDURE delete_data();' AS trigger_creation_query
FROM (
SELECT
quote_ident(table_schema) || '.' || quote_ident(table_name) as tab_name
FROM
information_schema.tables
WHERE
table_schema NOT IN ('pg_catalog', 'information_schema')
AND table_schema NOT LIKE 'pg_toast%'
) tablist;
This will get you set of strings which are SQL commands like:
CREATE TRIGGER schema1.table1 BEFORE DELETE ON ALL DATABASE FOR EACH ROW EXECUTE PROCEDURE delete_data();
CREATE TRIGGER schema1.table2 BEFORE DELETE ON ALL DATABASE FOR EACH ROW EXECUTE PROCEDURE delete_data();
CREATE TRIGGER schema1.table3 BEFORE DELETE ON ALL DATABASE FOR EACH ROW EXECUTE PROCEDURE delete_data();
CREATE TRIGGER schema2.table1 BEFORE DELETE ON ALL DATABASE FOR EACH ROW EXECUTE PROCEDURE delete_data();
CREATE TRIGGER schema2."TABLE2" BEFORE DELETE ON ALL DATABASE FOR EACH ROW EXECUTE PROCEDURE delete_data();
...
etc
You just need to run them at once (either by psql or pgAdmin).
Now some explanation:
I select names of tables in my database using information_schema.tables system table. Because there are data of literally all tables, remember to exclude pg_catalog and information_schema schemas and toast tables from your select.
I use quote_ident(text) function which will put string inside double quote signs ("") if necessary (ie. names with spaces or capital letters require that).
When I have list of tables names I just concatenate them with some static strings to get my SQL commands.
I write that command using sub-query because I want you to get better idea of what's going on here. You may write a single query by putting quote_ident(table_schema) || '.' || quote_ident(table_name) in place of tab_name.

Answer 2

A conveniently encapsulated version of Gabriel's answer. This time I am using the trigger to update a column named update_dt datetime granted to be part of any table in the public schema of the current database.
--
-- function: tg_any_update_datetime_fn
-- when: before insert or update
--
create or replace function tg_any_update_datetime_fn ()
returns trigger
language plpgsql as $$
begin
new.update_dt = now();
return new;
end;
$$;
--
-- function: ddl_create_before_update_trigger_on_all_tables
-- returns: Create a before update trigger on all tables.
--
create or replace procedure ddl_create_before_update_trigger_on_all_tables ()
language plpgsql as $$
declare
_sql varchar;
begin
for _sql in select concat (
'create trigger tg_',
quote_ident(table_name),
'_before_update before update on ',
quote_ident(table_name),
' for each row execute procedure tg_any_update_datetime_fn ();'
)
from
information_schema.tables
where
table_schema not in ('pg_catalog', 'information_schema') and
table_schema not like 'pg_toast%'
loop
execute _sql;
end loop;
end;
$$;
-- create before update trigger on all tables
call ddl_create_before_update_trigger_on_all_tables();
On my DDL scripts I use a large number of such ddl_ functions that have only meaning at DDL time. To remove them from the database use
--
-- function: ddl_drop_ddl_functions
-- returns: Drop all DDL functions.
-- since: 1.1.20
--
create or replace procedure ddl_drop_ddl_functions ()
language plpgsql as $$
declare
r record;
_sql varchar;
begin
for r in
select oid, prokind, proname
from pg_proc
where pronamespace = 'public'::regnamespace
and proname ilike 'ddl_%'
loop
case r.prokind
when 'a' then _sql = 'aggregate';
when 'p' then _sql = 'procedure';
else _sql = 'function';
end case;
_sql = format('drop %s %s', _sql, r.oid::regprocedure);
execute _sql;
end loop;
end
$$;