复杂的多列唯一约束

Question

我有一个10列的表，但只关心这3列。想象一下，我的表是这样的：

CREATE TABLE MyTable (RowID int IDENTITY(1,1), UserID int, NodeID int, RoleID int) 

我需要的是一个能够执行下列约束：用户ID和角色ID必须为每个节点ID是唯一的（即用户不能在多个节点的相同角色）。换句话说，我想允许

INSERT MyTable (UserID, NodeID, RoleID) SELECT 1, 1, 1 

但不允许

INSERT MyTable (UserID, NodeID, RoleID) SELECT 1, 2, 1 

如果第一次插入已经发生，因为这会导致在具有多个节点一个角色的用户。

希望这很简单，我只是把它比它需要在我的脑中更复杂。

Answer 1

由于您的约束取决于其他行数据的意见，这排除了过滤的索引。海事组织一个可行的选择可能是一个触发器。这样的触发器可能看起来像这样：

CREATE TRIGGER dbo.MyTrigger ON dbo.Q1 
    AFTER INSERT, UPDATE 
AS 
    DECLARE @userId INT, @Id INT, @roleId INT, @exists INT; 

    SELECT TOP 1 
      @userId = userID 
      ,@roleId = roleID 
      ,@Id = Id 
    FROM inserted;  

    SELECT TOP 1 
      @exists = Id 
    FROM Q1 
    WHERE userId = @userId 
      AND roleID = @roleID AND Id<> @Id;  

    IF ISNULL(@exists, 0) > 0 
     BEGIN   
      -- you would want to either undo the action here when you use an 'after' trigger 
      -- because as the name implies ... the after means the record is allready inserted/updated   
      RAISERROR ('No way we would allow this.', 16, 1); 
     END 
     -- else 
     -- begin 
      -- another alternative would be to use a instead of trigger, which means the record 
      -- has not been inserted or updated and since that type of trigger runs the trigger 'instead of' 
      -- updating or inserting the record you would need to do that yourself. Pick your poison ... 
     -- end 
GO 

Answer 2

的唯一索引应该执行你的要求

CREATE UNIQUE NONCLUSTERED INDEX [idx_Unique] ON [dbo].[MyTable] 
(
    [UserID] ASC, 
    [NodeID] ASC, 
    [RoleID] ASC 
) 

从我想你将需要两个唯一索引

CREATE UNIQUE NONCLUSTERED INDEX [idx_User_Node] ON [dbo].[MyTable] 
(
    [UserID] ASC, 
    [NodeID] ASC 
) 
GO 
CREATE UNIQUE NONCLUSTERED INDEX [idx_User_Role] ON [dbo].[MyTable] 
(
    [UserID] ASC, 
    [RoleID] ASC 
)