Question

我在数据库中有三个表是＆＃34; UserGroup＆＃34;它有一个独特的用户组。第二个表是＆＃34;用户＆＃34;具有用户但多个用户的用户可以属于同一用户组。

同样，我有第三张桌子＆＃34;角色＆＃34;包含角色和多个角色可以属于同一个＆＃34; usergroup＆＃34;。

因此父表是UserGroup，该表的id是另外两个表中的外键。

此处已经提出了相关问题，但如果您可以回答我的情况，那就更好了 Select from one table with count from two other tables

我正在尝试查询这些表，以便我需要计算＆＃34;用户组＆＃34;从两个表中的每一个，即来自＆＃34;用户＆＃34;和角色＆＃34;。如果您可以帮助Linq查询，我们将不胜感激。

例如：

＆＃34;用户组表＆＃34;

Id GroupName
1   Admin
2   IT
3   Helpdesk

＆＃34;用户表＆＃34;

Id USerGroupId UserName
1    1          Tom
2    1          Mickey
3    2          John
4    3          Sandy

＆＃34;角色表＆＃34;

Id  USerGroupId    Role
1     2            Supervisor 
2     2            Superidetendent
3     3            etc
4     3            etc

输出应显示：

GroupName     USerCount    RolesCount
Admin           2            0
IT              1            2
Helpdesk        1            2

Answer 1

SELECT GroupName 
,(SELECT COUNT*) FROM Users U WHERE U.USerGroupId=G.Id) [USerCount]   
,(SELECT COUNT*) FROM Roles r WHERE R.USerGroupId=G.Id) [RolesCount]  
FROM Group g

Answer 2

我觉得这样的事情应该有效：

UsersTable.GroupBy(u => u.USerGroupId).Select(group => new { 
                             USerGroupId = group.Key, 
                             Count = group.Count() 
                        }).OrderBy(x => x.USerGroupId);

RolesTable.GroupBy(u => u.USerGroupId).Select(group => new { 
                             USerGroupId = group.Key, 
                             Count = group.Count() 
                        }).OrderBy(x => x.USerGroupId);

Answer 3

这是c＃中的实体的linq（如果使用Entity Framework连接到DB）

var query = 
    from h in (
        (from b in db.UserTable
        group b.UserGroup by new {
          b.UserGroup.GroupName
        } into g
        select new {
          g.Key.GroupName,
          UserCount = g.Count(p => p.GroupName != null)
        }))
    join k in (
        (from d in db.Roles
        group d.UserGroup by new {
          d.UserGroup.GroupName
        } into g
        select new {
          g.Key.GroupName,
          RolesCount = g.Count(p => p.GroupName != null)
        })) on h.GroupName equals k.GroupName into k_join
    from k in k_join.DefaultIfEmpty()
    select new {
      h.GroupName,
      h.UserCount,
      RolesCount = k.RolesCount
    };

这是c＃中的linq to SQL（如果使用DBML）

var query = 
        from h in (
            (from a in db.UserGroup
            join b in db.UserTable on new { Id = a.Id } equals new { Id = b.UserGroupId } into b_join
            from b in b_join.DefaultIfEmpty()
            group a by new {
              a.GroupName
            } into g
            select new {
              g.Key.GroupName,
              UserCount = g.Count(p => p.GroupName != null)
            }))
        join k in (
            (from d in db.Roles
            group d.UserGroup by new {
              d.UserGroup.GroupName
            } into g
            select new {
              g.Key.GroupName,
              RolesCount = g.Count(p => p.GroupName != null)
            })) on h.GroupName equals k.GroupName into k_join
        from k in k_join.DefaultIfEmpty()
        select new {
          h.GroupName,
          h.UserCount,
          RolesCount = k.RolesCount
        };

这是源SQL

SELECT h.GroupName, h.UserCount, k.RolesCount
FROM
(SELECT a.GroupName, count(a.GroupName) as UserCount
from UserGroup a
LEFT JOIN UserTable b on a.id = b.UserGroupId
group by a.GroupName) h
LEFT JOIN (
SELECT a.GroupName, count(a.GroupName) as RolesCount
from UserGroup a
INNER JOIN Roles d on a.id = d.UserGroupId
group by a.GroupName) k on h.GroupName = k.GroupName

从其他表

3 个答案: