Question

SELECT COUNT(*) as totalHappenings FROM `happenings` WHERE `userId` = ? 
UNION 
SELECT COUNT(*) as xHappenings FROM `happenings` WHERE `userId` = ? AND `destinationObjectType` = \'2\' 
UNION 
SELECT COUNT(*) as yHappenings FROM `happenings` WHERE `userId` = ? AND `destinationObjectType` = \'1\'

由于它是同一个表，我不想通过3次userId参数如何才能解决这个问题？

Answer 1

您可以使用select子句中的if语句执行此操作：

  SELECT
    COUNT(userId) as totalHappenings, 
    SUM(IF(`destinationObjectType`='2',1,0) as xHappenings,
    SUM(IF(`destinationObjectType`='1',1,0) as yHappenings
  FROM `happenings`
  WHERE `userId` = ?

这肯定会在3列中返回您的结果。您的原始查询返回3行，但我认为这不是问题。

Answer 2

SELECT 
    COUNT(*) AS totalHappenings,
    SUM(CASE WHEN `destinationObjectType` = \'2\' THEN 1 ELSE 0 END) AS xHappenings, 
    SUM(CASE WHEN `destinationObjectType` = \'1\' THEN 1 ELSE 0 END) AS yHappenings 
FROM `happendings` 
WHERE `userId` = ?

结果：

totalHappenings xHappenings yHappenings
      24            10          14

Answer 3

尝试最短的方式：

SELECT COUNT(*) as totalHappenings, SUM(`destinationObjectType` = \'2\') AS xHappenings, SUM(`destinationObjectType` = \'1\') AS yHappenings FROM `happenings` WHERE `userId` = ?

SUM内的比较返回true或false（1或0），因此不需要IF或CASE语句

同桌数联盟

3 个答案: