mysql - 如何在mysql中只返回唯一值

Question

SELECT users.mail, users.name FROM members
LEFT JOIN users ON (users.uid = members.uid) WHERE members.group = 27
AND members.uid NOT IN (SELECT subgroup_members.uid FROM subgroup_members
LEFT JOIN subgroups ON (subgroups.id = subgroup_members.sid)
LEFT JOIN users on (users.uid = subgroup_members.uid) WHERE subgroups.oid = 27 AND subgroup_members.leader = 1)

此查询返回不是子组领导者的组的所有成员。

members表显示了哪个userid(uid)属于一个group(group)，subgroup_members表显示了哪些用户属于一个 subgroup(sid)。领导在 subgroup_members 表的领导列中用“1”表示。

我正在尝试弄清楚如何返回不是子组的唯一领导者的组的所有成员，我现在很困惑。

因此，我需要确定它是否是唯一值，而不是 subgroup_members.leader = 1

Answer 1

考虑使用 GROUP BY 来隔离唯一索引。

文档:https://dev.mysql.com/doc/refman/5.5/en/group-by-modifiers.html