SQL 交叉连接中的重复对？

Question

我知道 SO 上有很多类似的问题，我查看了其中的一些，即 this，但它不足以解决我的问题

我有一个 table proposals 看起来像这样：

proposalNum | PI        | department | investigator | investigatorDepartment|
---------------------------------------------------------------------------- 
FP00003521  | Bush,Raj  | GIS        | Amm,Anna     | CIS                   |
FP00003521  | Bush,Raj  | GIS        | Milton,Ross  | CIS                   |
FP00003521  | Bush,Raj  | GIS        | Landis, Amy  | SEB                   |
FP00069606  | Mill, Ash | DIA        | Keller, Bill | FAA                   |

我基本上想查看 investigator 字段并创建：

Amm,Anna     | Milton, Ross 
Amm,Anna     | Landis, Amy
Milton,Ross  | Landis, Amy

所有 CIS 的调查员，以及给定的 proposalNum（在本例中，FP00003521）

(这里是SQL FIDDLE)

我这样做了：

SELECT p1.investigator,p2.investigator
FROM proposals AS p1
CROSS JOIN proposals AS p2 
WHERE p1.investigatorDepartment='CIS' 
AND p1.investigator!=p2.investigator
AND p1.proposalNum=p2.proposalNum

并得到：

Milton,Ross  | Amm,Anna 
Amm,Anna     | Milton,Ross
Amm,Anna     | Landis, Amy
Milton,Ross  | Landis,Amy

但是那里有重复...

按照链接post上的逻辑，我也试过：

SELECT p1.investigator,p2.investigator
FROM proposals AS p1
CROSS JOIN proposals AS p2 
ON p1.investigator < p2.investigator
WHERE p1.investigatorDepartment='CIS' 
AND p1.investigator!=p2.investigator
AND p1.proposalNum=p2.proposalNum

我得到了这个：

Amm,Anna     | Milton,Ross
Amm,Anna     | Landis, Amy

问题是当我添加 ON p1.investigator < p2.investigator 条件时，它也不会添加 Milton,Ross 和 Landis, Amy，因为 M > L

我将如何重写我的查询来解决这个问题？

任何帮助将不胜感激，谢谢！！

Answer 1

您可以加入 p2's 独联体和非独联体的不同方式。一种方式如下。

select
  p1.investigator,
  p2.investigator
from
  proposals AS p1
    cross join
  proposals AS p2 
where
  p1.investigatorDepartment = 'CIS' and ((
      p2.investigatorDepartment = 'CIS' and 
      p1.investigator < p2.investigator
  ) or (
      p2.investigatorDepartment != 'CIS' or
      p2.investigatorDepartment is null
  )) and
  p1.proposalNum = p2.proposalNum;

SQL Fiddle

SQL 交叉连接中的重复对？

Duplicate pairs in SQL cross join?

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