SQL：通过连接查找最大值并加入其他值

Question

我有一个与客户的“table-a”和一个与客户联系的“table-b”。我想选择每个客户并显示上次“通过电话与客户联系”和最后一次“客户访问”，以及一些< strong>来自table-b的信息。

表格设计如下：

表一：

number (PK) Name    Adress      
101         Bob     Street 1      
102         Peter   Street 

表-B：

number (PK) c-nr (FK)   type    date        free text
11111       101         visit   01.08.2016  text3     
11112       101         visit   20.08.2016  text2     
11113       102         phone   15.09.2016  text1     
11113       102         email   15.09.2016  text1    

我想查询如下：

Number Name     Adress      Last Visit  Visit Text  Last-Call   Call-Text
101    Bob      Street  1   20.08.2016  text2       NONE        NONE                  
102    Peter    Street  2   NONE        NONE        15.09.206   text1     

到目前为止我得到的是：

select
a.number
,a.name
,a.adress
,last-visit.date
,last-call.date
from table-a as a
left join 
    (select
    inner-b.c-nr as customer-number
    ,max(inner-b.date) as date
    from table-b as inner-b
    where
    type = 'visit'
    group by innner-b.c-nr) as last-visit on last-visit.customer-number = a.number
left join 
    (select
    inner-b.c-nr as customer-number
    ,max(inner-b.date) as date
    from table-b as inner-b
    where
    type = 'phone'
    group by inner-b.c-nr) as last-call on last-call.customer-number = a.number

求助：

它可以显示我最后一次访问和最后一次调用，但我无法达到我可以添加文本的程度，因为如果我添加其他字段（即主键或文本本身） ）在内部选择它会搞砸组。此外，我不确定这是“好SQL”。

有什么建议吗？

Answer 1

您可以使用OUTER APPLY获取最新的visit，phone事件：

SELECT  a.number,
        a.[Name],
        a.Adress,
        CASE WHEN b.[type] = 'visit' THEN b.[date] ELSE NULL END as [Last Visit],
        CASE WHEN b.[type] = 'visit' THEN b.[free text] ELSE NULL END as [Visit Text],
        CASE WHEN c.[type] = 'phone' THEN c.[date] ELSE NULL END as [Last-Call],
        CASE WHEN c.[type] = 'phone' THEN c.[free text] ELSE NULL END as [Call-Text]
FROM tableA a
OUTER APPLY (
    SELECT TOP 1 *
    FROM TableB
    WHERE [c-nr] = a.number and [type] IN ('visit' )
    ORDER BY [date] desc
) b
OUTER APPLY (
    SELECT TOP 1 *
    FROM TableB
    WHERE [c-nr] = a.number and [type] IN ('phone')
    ORDER BY [date] desc
) c

您提供的样本的输出：

number  Name    Adress      Last Visit  Visit Text  Last-Call   Call-Text
101     Bob     Street 1    20.08.2016  text2       NULL        NULL
102     Peter   Street      NULL        NULL        15.09.2016  text1

Answer 2

你生活中需要row_number：

select a.number, 
       a.name, 
       a.Address,
       b.date as CallDate, 
       b.freetext as CallNotes, 
       c.date as VisitDate, 
       c.freetext as VisitNotes
from TableA a
left join 
    (
        select c_nr, date, freetext, row_number() over(partition by c_nr order by date desc) as Call_Ord
        from TableB
        where type = 'Phone'
    ) b
    on a.number = b.c_nr
    and b.Call_Ord = 1
left join 
    (
        select c_nr, date, freetext, row_number() over(partition by c_nr order by date desc) as Call_Ord
        from TableB
        where type = 'Visit'
    ) c
    on a.number = c.c_nr
    and c.Vis_Ord = 1

Answer 3

SQL DEMO

WITH lastVisit as (
      SELECT [c-nr], date, [free text],
             row_number() over (partition by [c-nr] order by [date] desc) rn
      FROM table_b
      WHERE type = 'visit'
 ), lastCall as (
      SELECT [c-nr], date, [free text],
             row_number() over (partition by [c-nr] order by [date] desc) rn
      FROM table_b
      WHERE type = 'phone'
 )
 SELECT ta.[number], ta.Name, ta.[Adress],
        COALESCE(lv.date, 'NONE') as [Last Visit],
        COALESCE(lv.[free text], 'NONE') as [Visit Text],

        COALESCE(lc.date, 'NONE') as [Last Call],
        COALESCE(lc.[free text], 'NONE') as [Call Text]

 FROM table_a ta
 LEFT JOIN lastVisit lv
   ON ta.[number] = lv.[c-nr]
  AND lv.rn = 1
 LEFT JOIN lastCall lc
   ON ta.[number] = lc.[c-nr]
  AND lc.rn = 1

<强>输出