SQL group by “column name”

Question

I cant seem to see why this query is failing, in my group by clause I have the columns that are in my select yet im still getting the error. Why is this? Below is my query;

SELECT c.customer_first_name, c.customer_last_name, MAX(SUM(cost_line))
FROM customers c LEFT OUTER JOIN orders o USING(customer_numb)
LEFT OUTER JOIN order_lines l USING (order_numb)
GROUP BY c.customer_first_name, c.customer_last_name
ORDER BY customer_numb;

getting this error

SQL Error: ORA-00937: not a single-group group function
00937. 00000 -  "not a single-group group function"

Answer 1

You need to get rid of the l.cost_line in the GROUP BY, as mti2935 suggests, and also get rid of the max() function -- you can't use multiple aggregate functions like this.

SELECT c.customer_first_name, c.customer_last_name, SUM(cost_line)
FROM customers c LEFT OUTER JOIN orders o USING(customer_numb)
LEFT OUTER JOIN order_lines l USING (order_numb)
GROUP BY c.customer_first_name, c.customer_last_name
ORDER BY customer_numb;

http://sqlfiddle.com/#!2/fdbba1/6

Answer 2

I think the problem is that you should not have l.cost_line in the GROUP BY clause, because you are using this field in an aggregate function in the SELECT clause. Try it without l.cost_line in the GROUP BY clause, and see if that solves the problem.

Answer 3

If you want the max value, you have to wrap it all up in subquery, take a look:

SELECT c.customer_first_name, c.customer_last_name, SUM(cost_line)
FROM customers c LEFT OUTER JOIN orders o USING(customer_numb)
LEFT OUTER JOIN order_lines l USING (order_numb)
GROUP BY c.customer_first_name, c.customer_last_name
HAVING SUM(cost_line) = (
  SELECT MAX(sum_cost_line)
    FROM
    (SELECT SUM(cost_line) sum_cost_line
      FROM customers c LEFT OUTER JOIN orders o USING(customer_numb)
        LEFT OUTER JOIN order_lines l USING (order_numb)
      GROUP BY c.customer_first_name, c.customer_last_name) a
  )
ORDER BY customer_numb;

Edit if you are using Oracle, you can make it simpler:

SELECT c.customer_first_name, c.customer_last_name, SUM(cost_line)
    FROM customers c LEFT OUTER JOIN orders o USING(customer_numb)
    LEFT OUTER JOIN order_lines l USING (order_numb)
    GROUP BY c.customer_first_name, c.customer_last_name
    HAVING SUM(cost_line) = (
      SELECT MAX(SUM(cost_line))
          FROM customers c LEFT OUTER JOIN orders o USING(customer_numb)
            LEFT OUTER JOIN order_lines l USING (order_numb)
          GROUP BY c.customer_first_name, c.customer_last_name
      )
    ORDER BY customer_numb;