php - 避免查询的空结果

Question

假设这个

用户表:[id] [邮件] [密码]

发生表:[id] [uid] [日期] [内容]

投票表[uid] [hid] [类型] [日期时间]

1 位用户可以有 0 次或更多次发生，1 次发生可以有 0 次或多次投票..

我想获得特定事件的总票数

SELECT
 H.*,
 SUM(CASE WHEN V.type='C' THEN 1 ELSE 0 END) AS upvotes,
 SUM(CASE WHEN V.type='R' THEN 1 ELSE 0 END) AS downvotes
FROM
 happens H
LEFT JOIN
 votes AS V
 ON V.hid = H.id
WHERE
 H.uid = :uid

问题是，如果没有投票与事件相关联，我从 mysql 得到一个空行，不是 EMPTY 而是 NULL

我怎样才能避免这个空结果？

[编辑]

一些尝试:

基本

SELECT H.* FROM happens H LEFT JOIN votes AS V ON V.hid = H.id WHERE H.uid = '178d937'

结果 -> 空

所有其他尝试使用 SUM、COUNT、HAVING 等给出:

[id] [uid] [what] [latitude] [longitude] [date] [time] [hide] [upvotes] [downvotes]
NULL NULL   NULL    NULL    NULL    NULL    NULL    NULL    0   0

Answer 1

使用HAVING检查空值

SELECT
 H.*,
 SUM(CASE WHEN V.type='C' THEN 1 ELSE 0 END) AS upvotes,
 SUM(CASE WHEN V.type='R' THEN 1 ELSE 0 END) AS downvotes
FROM
 happens H
LEFT JOIN
 votes AS V
 ON V.hid = H.id
WHERE
 H.uid = :uid
HAVING upvotes IS NOT NULL