Question

我是SQL新手，需要一些帮助。

我的SQL Server 2008数据库中有3个表。在每个表中有不同类型的用户（同事，学生，教师）。他们都有昵称。还有一个包含所有用户的表格。

我想将所有这些连接到一个表中，其中一列名为nickname。在本专栏中，三种不同类型的用户应该按照这样的包装进行排序，而不管他们的昵称是什么：

coworker1 coworker2 coworker2 student1 student2 student3 teacher1 teacher2

我尝试了以下方式：

SELECT A.Nickname, B.Nickname, C.Nickname, D.Nickname
FROM users AS A LEFT OUTER JOIN coworkers AS B ON
A.Nickname = B.Nickname
LEFT OUTER JOIN teachers AS C ON
A.Nickname = C.Nickname
LEFT OUTER JOIN students AS D ON
A.Nickname = D.Nickname

那根本不起作用，给我一个包含4列的表，每列都有NULL和未排序的用户

感谢HABO，我为它做了这件事：

select Nickname from (
  SELECT Coalesce( B.Nickname, C.Nickname, D.Nickname, A.Nickname ) as Nickname,
    case
      when B.Nickname is not NULL then 1
      when C.Nickname is not NULL then 3
      when D.Nickname is not NULL then 2
      else 0 end as Package
  FROM users AS A LEFT OUTER JOIN coworkers AS B ON
  A.Nickname = B.Nickname
  LEFT OUTER JOIN teachers AS C ON
  A.Nickname = C.Nickname
  LEFT OUTER JOIN students AS D ON
  A.Nickname = D.Nickname ) as Elmer
order by Package, Nickname

Answer 1

听起来你只能union和order三个用户类型表，而不是做一堆连接。

尝试这样的事情：

SELECT s.nickname nickname, ..., 'student' type FROM students s
UNION
SELECT t.nickname nickname, ..., 'teacher' type FROM teachers t
UNION
...
ORDER BY type;

这更接近你想要完成的事情吗？

Answer 2

如果您只想要非NULL列输出：

SELECT Coalesce( B.Nickname, C.Nickname, D.Nickname, A.Nickname ) as Nickname
FROM users AS A LEFT OUTER JOIN coworkers AS B ON
A.Nickname = B.Nickname
LEFT OUTER JOIN teachers AS C ON
A.Nickname = C.Nickname
LEFT OUTER JOIN students AS D ON
A.Nickname = D.Nickname

请注意，已重新排列列，以便users中的昵称是最后一个选择。

关于分拣包裹的评论我不清楚。你的意思是这样的：

select Nickname from (
  SELECT Coalesce( B.Nickname, C.Nickname, D.Nickname, A.Nickname ) as Nickname,
    case
      when B.Nickname is not NULL then 1
      when C.Nickname is not NULL then 3
      when D.Nickname is not NULL then 2
      else 0 end as Package
  FROM users AS A LEFT OUTER JOIN coworkers AS B ON
  A.Nickname = B.Nickname
  LEFT OUTER JOIN teachers AS C ON
  A.Nickname = C.Nickname
  LEFT OUTER JOIN students AS D ON
  A.Nickname = D.Nickname ) as Elmer
order by Package, Nickname

在一列中加入3个表并对其进行排序

2 个答案: