如何根據按不同對分組的列值來選擇行？

Question

我在我的數據庫中的以下信息：

TO | FROM | DATE | PRICE 
AAA | BBB | 12/3/2012 | $100 
AAA | CCC | 12/3/2010 | $200 
AAA | BBB | 10/3/2010 | $450 
BBB | CCC | 09/7/2010 | $270 
BBB | AAA | 06/9/2011 | $130 
AAA | CCC | 12/3/2013 | $176 

我想編寫一個查詢（或LINQ表達最好）至 - 自對，所以基於表上面我想要的是選擇最近的以下數據在我的查詢中返回：

TO | FROM | DATE | PRICE 
AAA | BBB | 12/3/2012 | $100 
BBB | CCC | 09/7/2010 | $270 
BBB | AAA | 06/9/2011 | $130 
AAA | CCC | 12/3/2013 | $176 

要做到這一點，最好的方法是什麼？

Answer 1

既然你沒有提到你的RDBMS，下面的查詢工作在最RDBMS

SELECT a.* 
FROM tableName a 
     INNER JOIN 
     (
      SELECT To, FROM, MAX(DATE) maxDate 
      FROM tableName 
      GROUP BY To, FROM 
     ) b ON a.To = b.To AND 
       a.FROM = b.FROM AND 
       a.DATE = b.maxDATE 

• SQLFiddle Demo Link

但如果你RDBMS支持CTE和WINDOWS FUNCTION

WITH latestRecord AS 
(
SELECT [To], [FROM], DATE, Price, 
     ROW_NUMBER() OVER (Partition BY [TO], [FROM] ORDER BY date DESC) rn 
FROM tableName 
) 
SELECT [To], [FROM], DATE, Price 
FROM latestRecord 
WHERE rn = 1 

• SQLFiddle Demo Link

或WINDOWS FUNCTION ONLY

SELECT [To], [FROM], DATE, Price 
FROM 
(
    SELECT [To], [FROM], DATE, Price, 
      ROW_NUMBER() OVER (Partition BY [TO],[FROM] ORDER BY date DESC) rn 
    FROM tableName 
) s 
WHERE rn = 1 

• SQLFiddle Demo Link

還有一點需要指出的是，TO和FROM有些保留關鍵字，它們必須用轉義字符轉義這取決於您正在使用的RDBMS。