Question

我发现了很多类似的话题，但我无法理解这些话题，无法解决我的具体案例。

A有一个包含以下基本结构的表：

+------------------------+
| id | session ID | bal  |
+------------------------+
| 0  | 00000002 | 100    |
| 1  | 00000002 | 120    |
| 2  | 00000002 | 140    |
| 3  | 00000001 | 900    |
| 4  | 00000001 | 800    |
| 5  | 00000001 | 500    |
+------------------------+

我需要创建一个（Microsoft SQL）查询，该查询根据顺序值返回每个唯一的sessionID以及第一个（＆＃34; start＆＃34;）和last（＆＃34; end＆＃34;）bal条目ID列的。结果如下：

+---------------------------+
| session ID | start | end  |
+---------------------------+
| 00000002   | 100   | 140  |
| 00000001   | 900   | 500  |
+---------------------------+

我怎样才能做到这一点？

Answer 1

编辑在回复您的评论时，SQL Server支持窗口功能。查找每bal的第一个和最后Session ID个值的一种方法是：

select  distinct [Session ID]
,       first_value(bal) over (partition by [Session ID] order by id) as [start]
,       first_value(bal) over (partition by [Session ID] order by id desc) as [end]
from    Table1

Example at SQL Fiddle.

另一种方式（有许多方法）是增加和减少行数：

select  [Session ID]
,       max(case when rn1 = 1 then bal end) as [start]
,       max(case when rn2 = 1 then bal end) as [end]
from    (
        select  row_number() over (partition by [Session ID] order by id) as rn1
        ,       row_number() over (partition by [Session ID] order by id desc) as rn2
        ,       *
        from    Table1
        ) as SubQueryAlias
group by
        [Session ID]

Example at SQL Fiddle.

Answer 2

您可以使用JOIN和Common Table Expression来提高可读性：

with CTE as
(
    select 
        sessionId, min(id) as firstId, max(id) as lastId
    from 
        log
    group by sessionId
)
select
    CTE.sessionId, Log1.bal as start, Log2.bal as [end]
from
    CTE
    join Log as Log1 on Log1.id = CTE.firstId
    join Log as Log2 on Log2.id = CTE.lastId

请参阅SQL Fiddle。

Answer 3

我认为bal是数字（虽然它不必在这种情况下，因为所有条目的长度都是3）

select sessionID
     , min(bal) as start
     , max(bal) as end
from table_name
group by sessionID

其中＆＃34; table_name＆＃34;是你的表的名称

Answer 4

在MySQL中可能是这样的：

SELECT `session ID`, MIN(bal) AS start, MAX(bal) AS end FROM `yourtable` WHERE `session ID` IN (
    SELECT DISTINCT(`session ID`) FROM `yourtable`
);

Answer 5

SELECT FIRST（column_name），LAST（column_name）FROM table_name; http://forums.mysql.com/read.php?65,363723,363723

从每个组的第一行和最后一行获取数据

5 个答案: