如何从查询结果中排除相等的值

Question

I have this query:

SELECT queue.first_dealer, queue.second_dealer, queue.status
FROM queue
WHERE queue.status = 3
AND queue.first_dealer = $user_id
OR queue.second_dealer = $user_id
AND queue.status = 3
ORDER BY id DESC
LIMIT 5

But sometimes the first_dealer or the second_dealer can be the same, I want to skip to the next records if they are the same.

Answer 1

You need to add some parentheses in your WHERE clause, because of [operator precedence][1] between AND and OR. Group conditions that belong together, together, like this:

SELECT queue.first_dealer, queue.second_dealer, queue.status
FROM queue
WHERE queue.status = 3
AND ( queue.first_dealer = $user_id 
      OR queue.second_dealer = $user_id)
AND queue.status = 3 AND 
queue.first_dealer <> queue.second_dealer
ORDER BY id DESC
LIMIT 5

Even in cases where you don't strictly need the parentheses, it may result in more readable code if you do.

Answer 2

SELECT queue.first_dealer, queue.second_dealer, queue.status
FROM queue
WHERE queue.status = 3
AND (queue.first_dealer = $user_id OR queue.second_dealer = $user_id)
AND queue.first_dealer != queue.second_dealer
AND queue.status = 3
ORDER BY id DESC
LIMIT 5

Answer 3

You should use parentheses in your WHERE statement:

WHERE queue.status = 3 and
      (queue.first_dealer = $user_id OR queue.second_dealer = $user_id)

If you don't want them to be the same, just add another clause:

WHERE queue.status = 3 and
      (queue.first_dealer = $user_id OR queue.second_dealer = $user_id) and
      queue.first_dealer <> queue.second_dealer