mysql - 主查询不返回记录时如何从子查询中获取计数

Question

当在主查询中找到记录时，下面的 MYSQL 查询为我提供了我需要的输出，例如

返回：

username  |  total_favs
this_user |  4

但是如果在主查询中没有找到任何记录，我什么也得不到。我想得到这样的东西：

返回：

username  |  total_favs
null |  4

SELECT 
  c.username,
  (SELECT COUNT(*) AS total_records FROM favourites f WHERE f.pic_id = 177) AS `total_favs`
FROM
  comments c
WHERE
  c.pic_id = 177

Answer 1

切换它favourites是主要查询：

SELECT c.username, COUNT(*) AS total_favs
FROM favourites f
LEFT OUTER JOIN comments c on f.pic_id = c.pic_id
WHERE f.pic_id = 177
GROUP BY c.username