如何在两列中选择最大值的记录？

Question

这个问题很难想出一个可以理解的标题。 我会尝试用一个例子来解释。

首先我有一个简单的表INFO Oracle数据库中：

year  type  message 
----  ----  ------- 
2001  1   cakes are yammy 
2003  2   apples are dangerous 
2012  2   bananas are suspicious 
2005  3   cats are tricky 

，我需要选择特定类型的最新消息（例如type = 1或type = 2）：所以我用

2001  1   cakes are yammy 
2012  2   bananas are suspicious 

查询（顺便说一句，在这种情况下是否正确？）：

select * from INFO i 
where year = (select max(year) from INFO i_last where i.type = i_last.type) 
and i.type in (1, 2) 

但现在我需要在我的INFO表中添加一个新的“季度”列。并按年份和季度选择最新的记录。

year  quarter  type  message 
----  -------  ----  ------- 
2001  2   1   cakes are yammy 
2012  3   2   onions are cruel 
2012  1   2   bananas are suspicious 
2005  1   3   cats are tricky 

1型或2的最新记录将是：

2001  2   1   cakes are yammy 
2012  3   2   onions are cruel 

我无法想象能做到这一点查询，并希望你能帮帮我吧。

Answer 1

分析功能，是你的朋友：

SELECT MAX(year ) KEEP (DENSE_RANK LAST ORDER BY year ASC, quarter ASC, message ASC) AS year, 
     MAX(quarter) KEEP (DENSE_RANK LAST ORDER BY year ASC, quarter ASC, message ASC) AS quarter, 
     MAX(message) KEEP (DENSE_RANK LAST ORDER BY year ASC, quarter ASC, message ASC) AS message, 
     type 
FROM  info 
GROUP BY type; 

SQLFIDDLE

Answer 2

给这一个镜头：

SELECT i.year, i.quarter, i.type, i.message 
FROM INFO i 
JOIN INFO iy 
    ON i.type = iy.type 
JOIN INFO iq 
    ON iq.type = iy.type  
WHERE i.type IN (1,2) 
GROUP BY i.year, i.quarter, i.type, i.message 
HAVING i.year = MAX(iy.year) AND i.quarter = MAX(iq.quarter)