Question

数据库中有3个表：

Users (UserID, UserName), Roles(RoleID, RoleName) and UserRoles(UserID, RoleID)

如何在具有IsAdmin列的Users表上创建视图，这里是一个模型：

CREATE VIEW UsersView AS
    SELECT
        u.UserID,
        u.UserName,
        CASE WHEN ur.RoleID IS NULL THEN (0) ELSE (1) END AS IsAdmin
    FROM Users AS u
        LEFT JOIN Roles AS r ON r.RoleName = N'Admins'
        LEFT JOIN UserRoles AS ur ON  ur.UserID = u.UserID
                                  AND ur.RoleID = r.RoleID

IsAdmin应该是（1）如果用户是“Admins”用户角色，而（0）如果他不是

Answer 1

试试这个

这是另一种方式......但我确实喜欢Charles Bretana发布的EXISTS版本

CREATE VIEW UsersView AS
SELECT UserID,UserName, MAX(IsAdmin) as IsAdmin
FROM(SELECT
    u.UserID,
    u.UserName,
    CASE r.RoleName when 'Admins' then 1 else 0 end AS IsAdmin
FROM Users AS u
    LEFT JOIN UserRoles AS ur ON ur.UserID = u.UserID
    LEFT JOIN Roles r on ur.RoleID = r.RoleID) x
    GROUP BY UserID,UserName

Answer 2

尝试：

  CREATE VIEW UsersView AS 
    SELECT 
        u.UserID, 
        u.UserName, 
        Case When Exists
           (Select * from userRoles ur
                Join Roles r On r.RoleId = ur.Roleid
            Where ur.userId = u.UserId
               And r.RoleName = '"Admins') 
          Then 1 Else 0 End IsAdmin 
    FROM Users u

Answer 3

这种方法很有效。注意添加新的角色检查是多么微不足道。

<强>代码

Declare @Users Table(UserID Int, UserName VarChar(256))
Declare @Roles Table(RoleID Int, RoleName VarChar(256))
Declare @UserRoles Table(UserID Int, RoleID Int)

Insert Into @Roles Select 1, 'Admins'
Insert Into @Roles Select 2, 'Role2'
Insert Into @Roles Select 3, 'Role3'
Insert Into @Roles Select 4, 'Genius'

Insert Into @Users Select 1, 'Phil'
Insert Into @UserRoles Select 1, 1
Insert Into @UserRoles Select 1, 2
Insert Into @UserRoles Select 1, 3
Insert Into @UserRoles Select 1, 4

Insert Into @Users Select 2, 'Jim'
Insert Into @UserRoles Select 2, 2
Insert Into @UserRoles Select 2, 3

Insert Into @Users Select 3, 'Susan'
Insert Into @UserRoles Select 3, 1
Insert Into @UserRoles Select 3, 2
Insert Into @UserRoles Select 3, 3


Select UserID,
       UserName,
       Cast([Admins] As Bit) As IsAdmin,
       Cast([Genius] As Bit) As IsGenius
From (
    Select  Users.UserID,
            Users.UserName,
            Roles.RoleName
    From @Users As Users
        Left Join @UserRoles As UserRoles On UserRoles.UserID = Users.UserID
        Left Join @Roles As Roles On UserRoles.RoleID = Roles.RoleID
) As Data
Pivot (
    Count(RoleName) For RoleName In (
        [Admins], [Genius]
    )
) As Result

<强>结果

UserID  UserName IsAdmin IsGenius
2       Jim      0       0
1       Phil     1       1
3       Susan    1       0

Answer 4

在Roles表中添加另一列isAdmin，并仅为Admin角色将其设置为true。然后，在视图等中，检查where子句中的isAdmin标记。

Answer 5

我自己的解决方案看起来更好。

视图中的一对多SELECT语句

5 个答案: