SQL aggregation query for SUM, but only allow positive sums (otherwise 0)

Question

I want to query an orders table and show the customer id and the total of all his orders, however the orders can have positive or negative totals.

select customer_id, SUM(order_total) from orders group by customer_id;

Now my question - how can I achieve the following in one sql query:

If the total sum is positive, I want to display it as is; if the total sum is negative, I just want to display 0 instead the actual amount.

What I am looking for is a function that can handle this, similar to the IFNULL function (IFNULL(SUM(order_total),0)), but instead of checking for null, it should check for a negative result.

Pseudo code:

IFNEGATIVE(SUM(order_total),0)

Is there a simple way in standard sql (or specifically in Mysql 5.5, would also be ok).

Answer 1

SELECT customer_id,
  CASE 
    WHEN SUM(order_total) < 0 THEN 0
    ELSE SUM(order_total)
  END
  FROM orders 
  GROUP BY customer_id;

Check your execution plan, but the 2 SUMs will probably be optimized to a single SUM under the hood.

Answer 2

Try with:

select customer_id, GREATEST( SUM(order_total),0) from orders group by customer_id;