Sql 将多行合并为一行

我有下表

Index    BookNumber  
  2         51 
  2         52 
  2         53 
  1         41  
  1         42 
  1         43

我试图得出以下结果

Index    BookNumber1  Booknumber2  Booknumber3  
----------------------------------------------
  1         41             42           43   
  2         51             52           53  

Index    BN1    BN2    BN3  
------------------------------
  1      41     null   null 
  1      null   42     null 
  1      null   null   43 
  2      51     null   null 
  2      null   52     null 
  2      null   null   53 

我能够提出以下查询，但是输出是意外的

SELECT DISTINCT 
    index,
    CASE WHEN index = 1 THEN Booknumber END AS BookNumber1,
    CASE WHEN index = 2 THEN Booknumber END AS BookNumber2,
    CASE WHEN index = 3 THEN Booknumber END AS BookNumber3
FROM Mytable;

我得到以下输出

Index    BookNumber1  Booknumber2  Booknumber3  
----------------------------------------------
  1         41             42           43   
  2         51             52           53  

Index    BN1    BN2    BN3  
------------------------------
  1      41     null   null 
  1      null   42     null 
  1      null   null   43 
  2      51     null   null 
  2      null   52     null 
  2      null   null   53 

---

是否有办法将其压缩为仅2行？

假设每个索引的书号始终为3或更少，您可以使用：

with data as
 (select idx,
         booknumber as bn1,
         lag(booknumber, 1) over(partition by idx order by idx, booknumber) as bn2,
         lag(booknumber, 2) over(partition by idx order by idx, booknumber) as bn3
    from books)
select *
  from data
 where data.bn1 = (select max(x.bn1) from data x where x.idx = data.idx)

---

SQLFIDLE演示在这里：

我不太确定查询中的索引如何与数据中的索引列匹配。但您需要的查询是：

SELECT index,
       max(CASE WHEN index = 1 THEN Booknumber END) AS BookNumber1 ,
       max(CASE WHEN index = 2 THEN Booknumber END) AS BookNumber2,
       max(CASE WHEN index = 3 THEN Booknumber END) AS BookNumber3
FROM Mytable
GROUP BY index;

给出您的数据后，查询看起来更像：

SELECT index,
       max(CASE WHEN ind = 1 THEN Booknumber END) AS BookNumber1 ,
       max(CASE WHEN ind = 2 THEN Booknumber END) AS BookNumber2,
       max(CASE WHEN ind = 3 THEN Booknumber END) AS BookNumber3
FROM (select mt.*, row_number() over (partition by index order by BookNumber) as ind
      from Mytable mt
     ) mt
GROUP BY index;

---

顺便说一下，索引是一个保留字，所以我假设它只是另一个列名的占位符。否则，您需要使用双引号或方括号对其进行转义。

不要忘记索引是一个保留字。就个人而言，我不喜欢使用保留字作为列名，但您可以使用方括号进行补偿，如我的示例中所示

这将在SQLServer2008中起作用+

declare @t table([Index] int, BookNumber int)
insert @t values
(2,51),(2,52),(2,53),(1,41),(1,42),(1,43)

;with cte as
(
select [Index], BookNumber, 
row_number() over (partition by [Index] order by BookNumber) rn
from @t
)
select [Index], [1] as Booknumber1, [2] as Booknumber2, [3] as Booknumber3
from cte
pivot (max([booknumber]) FOR [rn] IN ([1],[2],[3])) AS pvt 

结果:

Index Booknumber1 Booknumber2 Booknumber3
1     41          42          43
2     51          52          53

---

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