在纯SQL中对行进行分组

Question

我有一个包含日期和数字列的表，如下所示：

date        Number 
1-1-2012    1
1-2-2012    1
1-3-2012    2
1-4-2012    1

我想创建一个SQL查询，将具有相同Number的行分组并获取最小日期。仅当值iof Number与上一行/下一行相同时，才会发生分组。所以，结果是

date        Number 
1-1-2012    1
1-3-2012    2
1-4-2012    1

Cheerz，Lordkain

Answer 1

试试这个：

WITH   CTE AS(
       SELECT * ,ROW_NUMBER() OVER (ORDER BY [DATE] ) - 
                 ROW_NUMBER() OVER (PARTITION BY NUMBER ORDER BY [DATE] ) AS ROW_NUM
       FROM TABLE1)
SELECT NUMBER,MIN(DATE) AS DATE
FROM   CTE
GROUP BY ROW_NUM,NUMBER
ORDER BY DATE

SQL fiddle demo

Answer 2

SELECT Number, MIN(date)
FROM table
GROUP BY Number
ORDER BY Number

既然你的要求更具体一点，那怎么样？我自己没有检查过，但考虑到你的要求，可能会有所作为。

SELECT date, Number FROM (
SELECT Number, 
(SELECT MIN(date) FROM #table t2 WHERE t1.date <> t2.date AND t1.Number = t2.Number) AS date 
FROM table t1
) AS a
GROUP BY number, date