mysql - SQL 查询不工作。 Count 也应该返回零。但即使在外部加入后也不工作

Question

我在寻找这个小问题的解决方案时遇到了一些麻烦。我想得到团队的数量，我也需要零计数。如果我不提及特定的团队，这是有效的。但是当查询变得复杂时无法工作。

SELECT teams.name, COUNT(checkins.team_id) AS "count of checkins"
FROM checkins 
  RIGHT JOIN teams ON checkins.team_id = teams.id
GROUP BY checkins.team_id

这样修改后就失效了

SELECT teams.name, COUNT(checkins.team_id) AS "count of checkins"
FROM checkins 
  RIGHT JOIN teams ON checkins.team_id = teams.id
  WHERE checkins.team_id IN (1,3,2)
GROUP BY checkins.team_id

Answer 1

你可以试试这个:

SELECT teams.name, COUNT(checkins.team_id) AS "count of checkins"
FROM checkins 
  RIGHT JOIN teams ON checkins.team_id = teams.id
  WHERE (checkins.team_id IN (1,3,2) OR checkins.team_id IS NULL )
GROUP BY checkins.team_id