Question

我有一个名为TransferRequest的表，其中有两列是（receivingPrison，currentPrison）。他们都引用一个表监狱与列（prisonID，位置）。我需要进行某种联接才能显示“地点”。两个监狱，例如。结果：＆＃34;华盛顿＆＃34;，＆＃34;纽约＆＃34;。我知道我可以从一张桌子上获取位置：

SELECT Prison.location  
FROM Prison
JOIN TransferRequest
ON Prison.prisonID = TransferRequest.currentPrison;

和

SELECT Prison.location  
FROM Prison
JOIN TransferRequest
ON Prison.prisonID = TransferRequest.receivingPrison;

但是我不确定如何对同一类型的表中的两个相同类型的项执行SELECT。得到这张桌子怎么办？（标题：当前位置，接收位置）。

Answer 1

也许我错过了一些东西，但是如果你只想获得当前和接收监狱的位置名称，你可以通过加入prison表两次获得它们：

SELECT 
  rec_prison.location as 'Recieving Location',
  cur_prison.location as 'Current Location'
FROM TransferRequest tr
INNER JOIN Prison rec_prison 
  ON rec_prison.prisonID = tr.receivingPrison 
INNER JOIN Prison cur_prison 
  ON cur_prison.prisonID = tr.currentPrison;

Sample SQL Fiddle

Answer 2

相关的子查询可以做到：

SELECT P1.location AS location1

, (SELECT Prison.location  
FROM Prison
JOIN TransferRequest
ON Prison.prisonID = TransferRequest.receivingPrison ) AS location2

FROM Prison P1
JOIN TransferRequest T1
   ON P1.prisonID = T1.currentPrison;

Answer 3

您可以使用：

SELECT (SELECT       prison.Location
        FROM         TransferRequest tr
        INNER JOIN   Prison prison ON tr.reciveingPrisonID = prison.prisonID
        WHERE        tr.reciveingPrisonID = 1) AS'Recieving Location',
       (SELECT       prison.Location
        FROM         TransferRequest tr
        INNER JOIN   Prison prison ON tr.currentPrisonID = prison.prisonID
        WHERE        tr.currentPrisonID = 4) as 'Current Location'

在此处查看 - ＆gt; http://sqlfiddle.com/#!3/9aac5/9

希望这有帮助!!!

从同一个表的两行中选择数据

3 个答案: