Must I use inner join if I want to use MAX() value as a "where" condition? - sql

Question

My table is like this:
ProductID ProductName SupplierID CategoryID Unit Price
1 Chais 1 1 10 boxes x 20 bags 18
2 Chang 1 1 24 - 12 oz bottles 19
3 Aniseed Syrup 1 2 12 - 550 ml bottles 10
4 Chef Anton's
Cajun Seasoning 2 2 48 - 6 oz jars 21.35
5 Chef Anton's
Gumbo Mix 2 2 36 boxes 25
I copy it from https://www.w3schools.com/sql/sql_func_max.asp
I tried the simple version of MAX() function test, it works. But when I use the HighestPrice in the WHERE condtion as following:
SELECT
MAX(Price) AS HighestPrice,
SupplierID
FROM Products
GROUP BY SupplierID
WHERE HighestPrice>20;
The sytem report ERROR as:
Error: misuse of aggregate: MAX()
Does it mean I must use inner join to get what I want?

Answer 1

Following query should work:
SELECT SupplierID, MAX(Price) AS HighestPrice
FROM Products
GROUP BY SupplierID
HAVING MAX(Price) > 20;
following is the correct syntax of writing any SQL query:
SELECT column_name1,
SUM(column_name2)
FROM table_name
WHERE [CONDITION]
GROUP BY column_name1
HAVING (arithematic function condition);

Answer 2

Use having instead of where .
Where is always used before group by statement. It is way to filter the data which is already available with us whereas having is used after group by statement because it is applied on the data which we are in process of making.
SELECT MAX(Price) AS HighestPrice, SupplierID
FROM Products
Group By SupplierID
having MAX(Price) > 20;
Let me know in case of any queries.

Answer 3

Just for fun. If you specifically want to use where condition for highest price instead of having clause as given by G.arima with max function again. Do this:-
SELECT *
FROM
(
SELECT
MAX(Price) AS HighestPrice,
SupplierID
FROM Products
GROUP BY SupplierID
) a
WHERE HighestPrice>20;
Hope it helps :-)

Answer 4

By way of explanation of G.arima’s answer above:
When you use GROUP BY, you effectively create a new virtual table which contains only the GROUP BY fields as well as summaries.
There are two filter clauses, WHERE and HAVING, but they have a distinct role.
WHERE filters the original table. This gives you the formula FROM … WHERE …
HAVING filters the groups. This gives you the formula GROUP BY … HAVING …
What you ask is OK, but the clause is the wrong one. As G.arima says, you should use HAVING.