Error code 1111: says invalid use of group function - mysql

Question

Im trying to use
select Suppliers.sid
from Suppliers
left join Catalog on Suppliers.sid=Catalog.sid
where Catalog.cost>avg(Catalog.cost);
but im getting error code 1111:
Unsure what's going on with my database. Im very nice to sql and just having issues getting this to work.
CREATE DATABASE CSC123Lab2;
USE CSC123Lab2;
CREATE TABLE Suppliers (
sid CHAR(20),
sname CHAR(20),
address CHAR(20),
pid CHAR(20)
);
CREATE TABLE Parts (
pid CHAR(20),
pname CHAR(20),
color CHAR(20),
sid CHAR(20)
);
CREATE TABLE Catalog (
sid CHAR(20),
pid CHAR(20),
cost REAL
);
ALTER TABLE Suppliers ADD PRIMARY KEY (sid);
ALTER TABLE Parts ADD PRIMARY KEY (pid);
INSERT INTO Suppliers (sid, sname, address) VALUES (1, "carvel", "1234 Main Street");
INSERT INTO Suppliers (sid, sname, address) VALUES (2, "coldstone", "5678 Pine Street");
INSERT INTO Suppliers (sid, sname, address) VALUES (3, "ralphs", "9876 Oak Street");
INSERT INTO Suppliers (sid, sname, address) VALUES (4, "Acme Widget", "4321 Maple Street");
INSERT INTO Parts (pid, pname, color) VALUES (1, "hammer", "red");
INSERT INTO Parts (pid, pname, color) VALUES (2, "screwdriver", "pink");
INSERT INTO Parts (pid, pname, color) VALUES (3, "nails", "green");
INSERT INTO Parts (pid, pname, color) VALUES (4, "screws", "teal");
INSERT INTO Catalog (sid, pid, cost) VALUES (1, 3, 32);
INSERT INTO Catalog (sid, pid, cost) VALUES (4, 1, 10);
INSERT INTO Catalog (sid, pid, cost) VALUES (4, 3, 48);
INSERT INTO Catalog (sid, pid, cost) VALUES (2, 4, 24);
select Suppliers.sid
from Suppliers
left join Catalog on Suppliers.sid=Catalog.sid
where Catalog.cost>avg(Catalog.cost);
DROP TABLE Catalog;
DROP TABLE Parts;
DROP TABLE Suppliers;
DROP DATABASE CSC123Lab2;

Answer 1

use group by and do filter in next level
with cte as
(select Suppliers.sid,avg(Catalog.cost) as avg_val
from Suppliers
left join Catalog on Suppliers.sid=Catalog.sid
group by Suppliers.sid
) select a.sid
from Catalog a join cte on a.sid=cte.sid
where a.cost>avg_val

Answer 2

I think you just want a window function:
select s.sid
from Suppliers s join
(select c.*, avg(c.cost) over () as avg_cost
from Catalog c
) c
on s.sid = c.sid
where c.cost > c.avg_cost;
Note, though, that you don't really need the left join. The where clause turns the left join into an inner join.
Then, you don't need the join at all, because sid is in both tables:
select c.sid
from (select c.*, avg(c.cost) over () as avg_cost
from Catalog c
) c
where c.cost > c.avg_cost;
If you prefer, you could express this using a subquery:
select c.sid
from Catalog c
where c.cost > (select avg(c2.cost) from catalog c2);