按别名分组

问题描述

|

SELECT COALESCE (rsu.last_name + \',\' + rsu.first_name + \' \' + rsu.middle_name + \'.\',rsu.last_name + \',\' + rsu.first_name)  as student_name,rsu.day_id
FROM roster_school_unattended rsu
GROUP BY student_name
ORDER BY rsu.day_id

不起作用。什么是最优雅的解决方法？ 编辑：结果集应该有这样的东西

Muster,Hans | 2011-11-01
Muster,Hans | 2011-11-02
Williams,Clay | 2011-10-01
Williams,Clay | 2011-10-02

首先按名称分组，然后为每个名称排序。     

解决方法

编辑：整个事情都被替换了，因为对问题的最新编辑表明不需要GROUP BY ... 没有为“优雅”做任何更改...

SELECT
  rsu.last_name + \',\' + rsu.first_name + COALESCE (\' \' + rsu.middle_name + \'.\',\'\') as student_name,rsu.day_id
FROM
  roster_school_unattended  AS [rsu]
ORDER BY
  rsu.last_name + \',\'\'),rsu.day_id

可能会更改“优雅” ...

WITH formatted_rsu AS
(
  SELECT rsu.last_name + \',rsu.day_id
  FROM   roster_school_unattended  AS [rsu]
)
SELECT   student_name,day_id
FROM     formatted_rus
ORDER BY student_name,day_id

另一种可能使用APPLY ...

SELECT      formatted_rsu.student_name,rsu.day_id
FROM        roster_school_unattended  AS [rsu]
CROSS APPLY (SELECT rsu.last_name + \',\'\') as student_name) AS [formatted_rsu]
ORDER BY    formatted_rsu.student_name,rsu.day_id

    ,进行子选择将使您避免键入两次：

select t.student_name,t.day_id
from (
  select COALESCE (rsu.last_name + \',\' + rsu.first_name + \' \' + rsu.middle_name + \'.\',rsu.last_name + \',\' + rsu.first_name) as student_name,rsu.day_id
  from roster_school_unattended rsu ) t
group by t.student_name
order by t.day_id

但是day_id仍然有问题-分组子句中未包含它，因此如果不使用汇总（例如MAX），就无法选择它。     ,您可以使用子查询：

select student_name,day_id
from (SELECT COALESCE (rsu.last_name + \',\' + rsu.first_name)  as student_name,rsu.day_id
FROM roster_school_unattended rsu
) as rows
GROUP BY student_name
ORDER BY day_id

    ,我会去：

SELECT
    rsu.last_name
    + \',\' + rsu.first_name
    + COALESCE ( \' \' + rsu.middle_name + \'.\',\'\'
               )
    AS student_name,rsu.day_id
FROM
    roster_school_unattended AS rsu
ORDER BY
    rsu.last_name,rsu.first_name,rsu.middle_name,rsu.day_id

    ,

CROSS APPLY

是您为非窗口表达式加别名的朋友：

SELECT this.student_name,MAX(rsu.day_id) AS day_id
FROM roster_school_unattended rsu
CROSS APPLY (
  SELECT COALESCE (
      rsu.last_name+\',\'+rsu.first_name+\' \'+rsu.middle_name+\'.\',rsu.last_name+\',\'+rsu.first_name
    )  AS student_name
  ) this
GROUP BY this.student_name
ORDER BY this.student_name,MAX(rsu.day_id)

（假设SQL2005及更高版本）。