如何添加两个SUM

Question

为什么以下不会工作？

SELECT SUM(startUserThreads.newForStartUser)+SUM(endUserThreads.newForEndUser) AS numNew ...

它返回一个空字符串.

以下是为我的数据集返回1:

SELECT SUM(startUserThreads.newForStartUser) AS numNew ...

如何正确添加两个总和？

整个东西:

SELECT t.*,
       COUNT(startUserThreads.id) + COUNT(endUserThreads.id)                     AS numThreads,
       SUM(startUserThreads.newForStartUser) + SUM(endUserThreads.newForEndUser) AS numNew
FROM   `folder` `t`
       LEFT OUTER JOIN `thread` `startUserThreads`
         ON ( `startUserThreads`.`startUserFolder_id` = `t`.`id` )
       LEFT OUTER JOIN `thread` `endUserThreads`
         ON ( `endUserThreads`.`endUserFolder_id` = `t`.`id` )
WHERE  user_id = :user

仅供参考,只有两个用户可以在我的模型中共享一个线程.这应该解释我的专栏名称

Answer 1

SELECT COALESCE(SUM(startUserThreads.newForStartUser),0)+COALESCE(SUM(endUserThreads.newForEndUser),0) AS numNew ...