Trigger keeps failing to compile. Claims table not found when table exists - sql

Question

All the tables that are called definitely exist. I double checked the spelling as well.
The errors sqldeveloper gives are not very helpful and I can't seem to figure out why this is failing. I am attempting to make a trigger which updates the top5restaurants table when a new review comes in. I have a procedure which parses the review and adds them to the rating table. The top5restaurant table maintains the restaurants with the 5 highest ratings.
drop view bestratings_rest;
create view bestratings_rest(rid, rate) as
(select distinct rid, max(stars) from rating
group by rid);
drop table top5restaurants;
create table top5restaurants(rid int);
insert into top5restaurants rid
select rid from
(select rid, rate from bestratings_rest r
order by r.rate asc)
where rownum <=5;
drop view top5rest;
create view top5rest as
select rid, best from(
select t.rid, best from top5restaurants t
inner join (select distinct rid, max(stars) as best from rating
group by rid) b
on t.rid = b.rid);
create or replace trigger top5_trigger
after insert on rating
for each row
declare
minrow top5rest%rowtype;
restrid restaurant.rid%type;
restname restaurant.name%type;
begin
insert into minrow
select rid, min(best) from top5rest;
insert into restname
select rid from restaurant
where :new.rid = restaurant.rid;
if :new.stars > minrow.best then
DELETE FROM top5restaurants
where top5restaurants.rid = :new.rid;
insert into top5restaurants values(rid);
end if;
end;
/
--
--
begin
update_reviews('Jade Court','Sarah M.', 4, '08/17/2017');
update_reviews('Shanghai Terrace','Cameron J.', 5, '08/17/2017');
update_reviews('Rangoli','Vivek T.',5,'09/17/2017');
update_reviews('Shanghai Inn','Audrey M.',2,'07/08/2017');
update_reviews('Cumin','Cameron J.', 2, '09/17/2017');
end;
/
select * from top5restaurants;
sqldeveloper outputs:
View BESTRATINGS_REST dropped.
View BESTRATINGS_REST created.
Table TOP5RESTAURANTS dropped.
Table TOP5RESTAURANTS created.
5 rows inserted.
View TOP5REST dropped.
View TOP5REST created.
Trigger TOP5_TRIGGER compiled
LINE/COL ERROR
7/5 PL/SQL: SQL Statement ignored
7/17 PL/SQL: ORA-00942: table or view does not exist
11/5 PL/SQL: SQL Statement ignored
11/17 PL/SQL: ORA-00942: table or view does not exist
18/5 PL/SQL: SQL Statement ignored
18/40 PL/SQL: ORA-00984: column not allowed here
Errors: check compiler log

Answer 1

You don't insert into a scalar variable. You can do a select into. The statement
select rid
into restname
from restaurant
where :new.rid = restaurant.rid;
is syntactically valid. But it is almost certainly incorrect. Presumably, you want to select the restaurant name not the rid
select name
into restname
from restaurant
where :new.rid = restaurant.rid;
If you declare a %rowtype variable, then you want to do a select * into that variable. Otherwise you'll get a compilation error in the future if anyone adds or removes a column. You'd have to add a predicate that specified which row you wanted to select. My guess is that you want something like this to give the row with the lowest best score (or the row with the lowest rid if there are two with the same low score
select *
into minrow
from top5rest low
where not exists( select 1
from top5rest high
where low.best > high.best )
and not exists( select 1
from top5rest same
where low.best = same.best
and low.rid > same.rid )
More fundamentally, though, even if you get your syntax errors corrected, you're going to get a runtime mutating table error if you try to query the rating table (which your view does) from inside a row-level trigger on the rating table. That's not allowed. It almost guarantees that you have a problem in your logic. In this case, there seems to be no need for a separate table to store the top 5 restaurants. Realistically, your view should just do that calculation if you need the results in real-time or you should create a materialized view that refreshes periodically if you don't need to see a restaurant's overall rating change instantly when new ratings are added. So you probably don't want a trigger at all.