三路全外连接/表合并

Question

我想在三个表上执行合并常用行的FULL OUTER JOIN。

SELECT * FROM Users 

id Username Fullname 
== ======== ===================== 
7 iboyd  Ian Boyd 
8 nicholle Nicholle Kuzniak 
10 jamie  Jamie Bellaire 

3 row(s) affected 


SELECT * FROM GrobUsers 

id Username Fullname 
== ======== ===================== 
7 iboyd  Ian Alexander Boyd 
8 nicholle Nicholle Bachand 
9 chris  Chris Windibank 

3 row(s) affected 


SELECT * FROM FrobUsers 

id Username Fullname 
== ======== ===================== 
7 ian  Ian 
9 chris  Chris W. 
10 jamie  James Bellaire 

3 row(s) affected 

我想根据id列合并表。

这带来了的我怎么 要解决冲突时，其他 列的值不同的问题。可应用于解决用户名和全名之间的冲突算法 是：

if (id's are equal) then 
    pick one; i don't care 

我试过沿着线的东西：

SELECT 
    COALESCE(Users.id, GrobUsers.id, FrobUsers.id) AS id, 
    COALESCE(Users.Username, GrobUsers.Username, FrobUsers.Username) AS Username, 
    COALESCE(Users.FullName, GrobUsers.FullName, FrobUsers.FullName) AS Fullname 
FROM Users 
    FULL OUTER JOIN GrobUsers ON GrobUsers.id = Users.id 

    FULL OUTER JOIN FrobUsers ON FrobUsers.id = .....something...... 

Answer 1

在这个例子中，你给你根本不需要连接。我希望，这是一个真实的例子，而不是人为的。你想做的事情在这里很简单，你根本不需要连接，你不需要row_number。你可以这样说：

select id,Username,Fullname from Users 
UNION ALL 
select id,Username,Fullname from GrobUsers 
where id not in (select id from Users) 
UNION ALL 
select id,Username,Fullname from FrobUsers 
where id not in (select id from Users) and id not in (select id from GrobUsers) 

，它会给你：

id   Username Fullname   
----------- ---------- ----------------- 
7   iboyd  Ian Boyd   
8   nicholle Nicholle Kuzniak 
9   chris  Chris Windibank 
10   jamie  Jamie Bellaire 

(4 row(s) affected) 

下面是测试情况下，我用：

IF EXISTS (SELECT * FROM sys.objects WHERE object_id = OBJECT_ID(N'[dbo].[Users]') AND type in (N'U')) 
DROP TABLE [dbo].[Users] 
GO 

IF EXISTS (SELECT * FROM sys.objects WHERE object_id = OBJECT_ID(N'[dbo].[GrobUsers]') AND type in (N'U')) 
DROP TABLE [dbo].[GrobUsers] 
GO 

IF EXISTS (SELECT * FROM sys.objects WHERE object_id = OBJECT_ID(N'[dbo].[FrobUsers]') AND type in (N'U')) 
DROP TABLE [dbo].[FrobUsers] 
GO 

CREATE TABLE [dbo].[Users](
    [Id] [int] NOT NULL, 
    [Username] [nchar](50) NULL, 
    [Fullname] [nchar](50) NULL, 
CONSTRAINT [PK_Users] PRIMARY KEY CLUSTERED 
(
    [Id] ASC 
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY] 
) ON [PRIMARY] 

GO 

CREATE TABLE [dbo].[GrobUsers](
    [Id] [int] NOT NULL, 
    [Username] [nchar](50) NULL, 
    [Fullname] [nchar](50) NULL, 
CONSTRAINT [PK_GrobUsers] PRIMARY KEY CLUSTERED 
(
    [Id] ASC 
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY] 
) ON [PRIMARY] 

GO 

CREATE TABLE [dbo].[FrobUsers](
    [Id] [int] NOT NULL, 
    [Username] [nchar](50) NULL, 
    [Fullname] [nchar](50) NULL, 
CONSTRAINT [PK_FrobUsers] PRIMARY KEY CLUSTERED 
(
    [Id] ASC 
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY] 
) ON [PRIMARY] 

GO 

INSERT INTO Users Values (7,'iboyd','Ian Boyd') 
INSERT INTO Users Values (8,'nicholle','Nicholle Kuzniak') 
INSERT INTO Users Values (10,'jamie','Jamie Bellaire') 


INSERT INTO [GrobUsers] Values (7,'iboyd','Ian Alexander Boyd ') 
INSERT INTO [GrobUsers] Values (8,'nicholle','Nicholle Bachand') 
INSERT INTO [GrobUsers] Values (9,'chris','Chris Windibank') 

INSERT INTO [FrobUsers] Values (7,'iboyd','Ian') 
INSERT INTO [FrobUsers] Values (9,'nicholle','Chris W.') 
INSERT INTO [FrobUsers] Values (10,'jamie','James Bellaire') 
GO 

Answer 2

一个典型的把戏 - 用聚合功能没有意义。

select id, min(username), min(fullname) from (
    SELECT * FROM Users 
    union 
    SELECT * FROM FrobUsers 
    union 
    SELECT * FROM GrobUsers 
) as foo 
group by foo.id 

嗯...但它可以从一个表中选择用户名，从另一个表中选择全名。如果你仍然不在意，使用它，否则...也许

select id, username, fullname from (
    select id, username, fullname, takeme = row_number() over (partition by id) 
    from (
    SELECT * FROM Users 
    union 
    SELECT * FROM FrobUsers 
    union 
    SELECT * FROM GrobUsers 
) as foo 
) as bar 
where bar.takeme = 1