php - 如何从查询结果中排除相等的值

Question

我有这个查询：

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

但有时 first_dealer 或 second_dealer 可以相同，如果它们相同，我想跳到下一条记录。

Answer 1

[operator precedence][1]由于AND 和 OR 之间，您需要在 WHERE 子句中添加一些括号。将属于一起的条件组合在一起，如下所示：

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

即使在您并不严格需要括号的情况下，如果您这样做，也可能会产生更具可读性的代码。

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

您应该在WHERE语句中使用括号：

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

如果您不希望它们相同，只需添加另一个子句：

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