1SELECT * FROM
2(SELECT [column] FROM [table]) a
3LEFT JOIN (SELECT [column1], [columnn2] FROM [table]) b
4ON a.column = b.column1
1SELECT * FROM
2(SELECT [UserID] FROM [User]) a
3LEFT JOIN (SELECT [TailUser], [Weight] FROM [Edge] WHERE [HeadUser] = 5043) b
4ON a.UserId = b.TailUser