check value in more than one inserted object Postgresql - sql

Question

What I want to achive is check if hours count in day is higher than 24.
For example:
I've got entity hour with fields:
Integer id;
LocalDate date;
Integer hours;
Now I use post method to add new objects for example:
I add first one:
id - 1
date - 22.08.2018
hours - 10
I add second one:
id - 2
date - 22.08.2018
hours - 10
I add thrid one (hours count is now higher than 24 so I need an exception to be thrown )
id - 3
date - 22.08.2018
hours - 10
What I already have:
<sql>
ALTER TABLE hours_worked ADD CONSTRAINT more_than24h CHECK (hours >=0 AND hours <= 24)
</sql>
But this one only checks if I'm not adding more than 24 at once.

Answer 1

you can use constraint to check OTHER rows - you need trigger here, example for insert:
t=# create table i (id int, h int);
CREATE TABLE
t=# insert into i values(1,10),(1,10),(2,23);
INSERT 0 3
t=# create or replace function fi() returns trigger as $$ begin
if (select sum(h)+NEW.h > 24 from i where id = NEW.id) then
raise exception '%','over 24 for '||NEW.id;
end if;
return NEW; end;
$$ language plpgsql
;
CREATE FUNCTION
t=# create trigger ti before insert ON i for each row EXECUTE PROCEDURE fi();
CREATE TRIGGER
t=# insert into i values(1,1);
INSERT 0 1
t=# insert into i values(1,1);
INSERT 0 1
t=# insert into i values(1,1);
INSERT 0 1
t=# insert into i values(1,1);
INSERT 0 1
t=# insert into i values(1,1);
ERROR: over 24 for 1
CONTEXT: PL/pgSQL function fi() line 3 at RAISE
of course you need similar for UPDATE