Question

我有一个设置表，可以显示为： object_id（int） key（varchar）价值（文字）

我正在尝试抓住具有等于2项的密钥的object_id。

SELECT `object_id` FROM `settings` WHERE `key` = 'A' AND `key` = 'B'

我知道这不起作用，我能想到的唯一方法是加入它自己：

SELECT a.`object_id` FROM `settings` AS a LEFT JOIN `settings` AS b ON ( a.`object_id` = b.`object_id` ) WHERE a.`key` = 'A' and b.`key` = 'B'

虽然我没有测试过最后一个声明，但我确信这样的事情可行。此查询将每小时在可能数十万条记录上执行，因此我希望保持优化 - 有更好的方法吗？

Answer 1

哦，你想要：

  SELECT `object_id` 
    FROM `settings`  
   WHERE (`key` = 'A' AND `value`='foo') 
      OR (`key`= 'B' AND `value`='bar')
GROUP BY `object_id`
  HAVING COUNT(*) = 2

使用：

  SELECT `object_id` 
    FROM `settings`  
   WHERE `key` IN ('A', 'B')
GROUP BY `object_id`
  HAVING COUNT(DISTINCT `key`) = 2

或者：

SELECT x.`object_id` 
  FROM `settings` AS x 
  JOIN `settings` AS y ON y.`object_id` = x.`object_id`  
 WHERE x.`key` = 'A' 
   AND y.`key` = 'B'

MySQL - 基于Key / Value表中的2个键加入表

1 个答案: