mysql - SQL #/count from inner join

Question

我有一个简单的查询:

SELECT games.*
FROM games 
INNER JOIN invitations ON invitations.game_id = games.id 

我想获得#(COUNT) 个游戏邀请。我不确定将计数语句放在哪里。

Answer 1

您将使用 count() 聚合函数并按游戏 ID 分组:

SELECT g.id, g.name, count(i.game_id) TotalInvitations
FROM games g
INNER JOIN invitations i
  ON i.game_id = g.id 
group by g.id, g.name

这也可以使用子查询来编写:

select g.*, i.TotalInvitations
FROM games g
INNER JOIN
(
  select game_id, count(game_id) TotalInvitations
  from invitations
  group by game_id
) i
  ON i.game_id = g.id