why does this give me the wrong customerNumber?

Question

I tried to get the customer that pay the maximum amount. It gave me the maximum amount but the wrong customer. what should i do?

SELECT temp.customerNumber, MAX         


        

Answer 1

Using a join, possibly as follows:-

SELECT *
FROM payments
INNER JOIN
(
    SELECT MAX(amount) AS MaxAmount
    FROM payments
) Sub1
ON payments.amount = Sub1.MaxAmount

Down side of this is that if 2 people both have the same high payment then both will be returned.

Answer 2

I don't think you need the Subquery here:

SELECT p.customerNumber, MAX(p.amount) AS max
FROM payments p
GROUP BY p.customerNumber
ORDER BY max DESC
LIMIT 1

Answer 3

Consider that your subselect will return something like

customerNumber amount
1              100
2              200

Then the outer query will pull up those customer numbers and the MAX of ALL the rows, which breaks the link between customer numbers and their respective amounts. You're forcing the LARGES amount from ALL of the groups to be applied to all of the groups:

cN   amount
1    200
2    200