如何在兩個SELECT語句之間執行SQL Server中的LEFT JOIN？

Question

我在SQL Server這樣的兩個SELECT語句：

(SELECT [UserID] FROM [User]) 
(SELECT [TailUser], [Weight] FROM [Edge] WHERE [HeadUser] = 5043) 

我想執行一個留在[用戶名]屬性和[TailUser]屬性這兩個SELECT語句之間的連接。我想在第二個查詢中加入第一個查詢中相應的記錄和缺省記錄的NULL值中的現有記錄。我怎樣才能做到這一點？

Answer 1

SELECT * FROM 
(SELECT [UserID] FROM [User]) a 
LEFT JOIN (SELECT [TailUser], [Weight] FROM [Edge] WHERE [HeadUser] = 5043) b 
ON a.UserId = b.TailUser 

Answer 2

select * 
from user 
left join edge 
on user.userid = edge.tailuser 
and edge.headuser = 5043 

Answer 3

SELECT [UserID] FROM [User] u LEFT JOIN (
SELECT [TailUser], [Weight] FROM [Edge] WHERE [HeadUser] = 5043) t on t.TailUser=u.USerID 

Answer 4

試試這個：不是WHERE

SELECT user.userID, edge.TailUser, edge.Weight 
FROM user 
LEFT JOIN edge ON edge.HeadUser = User.UserID 
WHERE edge.HeadUser=5043 

OR

AND edge.HeadUser=5043 

clausule。