Question

我正在开发一款应用。我必须查询我在哪里看到我是客人或管理员的房间。这很简单。问题是我想同时获得同一房间内的玩家数量。

SELECT rooms.id, rooms.name, rooms.buyin, rooms.administrator, rooms.creation_date,
       rooms.max_players, rooms.min_players, count(room_players.room)
FROM rooms, room_players
WHERE administrator = 1 and room_players.room = rooms.id

我有一个房间的桌子和另一个（room_players）用户和房间之间的匹配。如果我删除了count(room_players.room)和and room_players.room = rooms.id我有我管理的房间。但我也需要同一房间内的玩家数量。

Answer 1

您的查询需要group by。使用COUNT()中的select，它将成为一个返回一行的聚合查询 - 表中所有行的摘要。

SELECT r.id, r.name, r.buyin, r.administrator, r.creation_date,
       r.max_players, r.min_players, count(rp.room)
FROM rooms r join
     room_players rp
     ON rp.room = r.id 
WHERE administrator = 1 
GROUP BY r.id;

我还将连接语法修复为显式连接并添加了表别名以使查询更具可读性。

编辑：

我怀疑你想要的查询是这样的：

SELECT r.id, r.name, r.buyin, r.administrator, r.creation_date,
       r.max_players, r.min_players, count(rp.room)
FROM rooms r join
     room_players rp
     ON rp.room = r.id 
WHERE administrator <> 1 
GROUP BY r.id
HAVING sum(user = 1) > 0;

Answer 2

如何从总用户中减去管理员的数量？

MySQL查询错误COUNT

2 个答案: