Postgres exclude using gist across different tables - postgresql

Question

I have 2 tables like this
drop table if exists public.table_1;
drop table if exists public.table_2;
CREATE TABLE public.table_1 (
id serial NOT NULL,
user_id bigint not null,
status varchar(255) not null,
date_start date NOT NULL,
date_end date NULL
);
CREATE TABLE public.table_2 (
id serial NOT NULL,
user_id bigint not null,
status varchar(255) not null,
date_start date NOT NULL,
date_end date NULL
);
alter table public.table_1
add constraint my_constraint_1
EXCLUDE USING gist (user_id with =, daterange(date_start, date_end, '[]') WITH &&)
where (status != 'deleted');
alter table public.table_2
add constraint my_constraint_2
EXCLUDE USING gist (user_id with =, daterange(date_start, date_end, '[]') WITH &&)
where (status != 'deleted');
Every table contains rows which are related to a user, and all the rows of the same user cannot overlap in range. In addition, some rows may be logically deleted, so I added a where condition.
So far it's working w/o problems, but the 2 constraints work separately for each table.
I need to create a constraint which cover the 2 set of tables, so that a single daterange (of the same user and not deleted), may appaer only once across the 2 different tables.
Does the EXCLUDE notation be extended to work with different tables or do I need to check it with a trigger? If the trigger is the answer, which is the simplier way to do this? Create a temporary table with the union of the 2, add the constraint on it and check if fails?

Answer 1

Starting from #Laurenz Albe suggestion, this is what I made
-- #################### SETUP SAMPLE TABLES ####################
drop table if exists public.table_1;
drop table if exists public.table_2;
CREATE TABLE public.table_1 (
id serial NOT NULL,
user_id bigint not null,
status varchar(255) not null,
date_start date NOT NULL,
date_end date NULL
);
CREATE TABLE public.table_2 (
id serial NOT NULL,
user_id bigint not null,
status varchar(255) not null,
date_start date NOT NULL,
date_end date NULL
);
alter table public.table_1
add constraint my_constraint_1
EXCLUDE USING gist (user_id with =, daterange(date_start, date_end, '[]') WITH &&)
where (status != 'deleted');
alter table public.table_2
add constraint my_constraint_2
EXCLUDE USING gist (user_id with =, daterange(date_start, date_end, '[]') WITH &&)
where (status != 'deleted');
-- #################### SETUP TRIGGER ####################
create or REPLACE FUNCTION check_date_overlap_trigger_hook()
RETURNS trigger as
$body$
DECLARE
l_table text;
l_sql text;
l_row record;
begin
l_table := TG_ARGV[0];
l_sql := format('
select *
from public.%s as t
where
t.user_id = %s -- Include only records of the same user
and t.status != ''deleted'' -- Include only records that are active
', l_table, new.user_id);
for l_row in execute l_sql
loop
IF daterange(l_row.date_start, COALESCE(l_row.date_end, 'infinity'::date)) && daterange(new.date_start, COALESCE(new.date_end, 'infinity'::date))
THEN
RAISE EXCEPTION 'Date interval is overlapping with another one in table %', l_table
USING HINT = 'You can''t have the same interval across table1 AND table2';
END IF;
end loop;
RETURN NEW;
end
$body$
LANGUAGE plpgsql;
-- #################### INSTALL TRIGGER ####################
create trigger check_date_overlap
BEFORE insert or update
ON public.table_1
FOR EACH row
EXECUTE PROCEDURE check_date_overlap_trigger_hook('table_2');
create trigger check_date_overlap
BEFORE insert or update
ON public.table_2
FOR EACH row
EXECUTE PROCEDURE check_date_overlap_trigger_hook('table_1');
-- #################### INSERT DEMO ROWS ####################
insert into public.table_1 (user_id, status, date_start, date_end) values (1, 'active', '2020-12-10', '2020-12-20');
insert into public.table_1 (user_id, status, date_start, date_end) values (1, 'deleted', '2020-12-15', '2020-12-25');
insert into public.table_1 (user_id, status, date_start, date_end) values (2, 'active', '2020-12-10', '2020-12-20');
insert into public.table_1 (user_id, status, date_start, date_end) values (2, 'deleted', '2020-12-15', '2020-12-25');
-- This will fail for overlap on the same table
-- insert into public.table_1 (user_id, status, date_start, date_end) values (1, 'active', '2020-12-15', '2020-12-25');
-- This will fail as the user 1 already has an overlapping period on table 1
-- insert into public.table_2 (user_id, status, date_start, date_end) values (1, 'active', '2020-12-15', '2020-12-25');
-- This will fail as the user 1 already has an overlapping period on table 1
insert into public.table_2 (user_id, status, date_start, date_end) values (1, 'deleted', '2020-12-15', '2020-12-25');
update public.table_2 set status = 'active' where id = 1;
select 'table_1' as src_table, * from public.table_1
union
select 'table_2', * from public.table_2

Answer 2

You can probably use a trigger, but triggers are always vulnerable to race conditions (unless you are using SERIALIZABLE isolation).
If your tables really have the same columns, why don't you use a single table (and perhaps add a type column to disambiguate)?