Question

I have this query, but it takes too long, approximately 30 seconds via NaviCat. How can it be optimized if it’s possible?

SELECT DISTINCT c.clientid, c.name, c.email, c.region 
FROM clients c RIGHT JOIN orders o ON c.clientid = o.clientid 
WHERE o.order_status = 'pending' 
AND c.clientid NOT IN (
    SELECT DISTINCT c.clientid 
    FROM clients c, orders o
    WHERE c.clientid = o.clientid AND o.order_status = 'paid'
    ) 
ORDER BY c.id DESC

To understand better what I need: I have 2 tables:

clients (id, clientid, name, email, region) 
orders (id, orderid, clientid, order_amount, order_status, ….)

Example of records:

Client | Order | Status
-----------------------
C1     | O1    | (paid)
C1     | O2    | (pending)
C2     | O3    | (paid)
C3     | O4    | (pending)
C4     | O5    | (paid)
C5     | O6    | (pending)

I need to return only C3 and C5

Many thanks for your answers.

Answer 1

There are lots of ways, here is one of the trick :-

SELECT c.clientid, c.name, c.email, c.region,
  SUM(IF(o.order_status = 'paid', 1, 0)) as paid
FROM clients c
INNER JOIN orders o 
ON c.clientid = o.clientid 
WHERE o.order_status IN( 'pending', 'paid')
GROUP BY c.clientid
HAVING paid = 0;