SQL Server以多行合併成一行，其中COL0 = COL1

Question

我的表：

previousid|CurrentID|Data 
| 1  | 2  | Data 1 
| 2  | 3  | Data 2 
| 3  | 4  | Data 3 
| 4  | 5  | Data 4 

結果，我去找：

Select .... where PreviousID=1 : 

    |Col0|Col1|Col2 |Col3|Col 4|Col5| Col6 | Col7 | Col8 
    |1 |2 |Data 1|3 |Data 2| 4 | data 3| 5 | data 4 

Select .....where PreviousID=2 

    |Col0|Col1|Col2 |Col3|Col 4|Col5| Col6 | 
    |2 |3 |Data 2|4 |Data 3| 5 | data 4| 

我試圖創造一些SQL服務器查詢來獲取結果和沒有運氣，請幫助我的傢伙

Answer 1

我們可以在幾個步驟做到這一點：

1. 聲明並設置一個變量來使用我們的根節點，並創建一個臨時表來存儲來自我們recusive查詢的結果：
2. 將結果從recusive查詢插入臨時表
3. 生成並執行動態sql到pivot()臨時表。
4. （候補）生成並執行動態SQL使用條件聚合代替pivot()：

rextester 演示：http://rextester.com/MRFZC75180

---

測試設置：

create table t (PreviousID int, CurrentID int, Data varchar(32)); 
insert into t values 
    (1,2,'Data 1'),(2,3,'Data 2'),(3,4,'Data 3'),(4,5,'Data 4'); 

1. 聲明並設置一個變量爲使用我們的根節點，並創建一個臨時表，用於存儲從我們的recusive查詢的結果：

declare @PreviousId int = 2; 

create table #temp (PreviousID int 
    , Level int 
    , Col varchar(32) 
    , Value varchar(32) 
    , rn int 
); 

插入來自recusive查詢結果到臨時表

個

;with cte as (
    select PreviousID, CurrentID, Data, level = 0 
    from t 
    where previousId = @PreviousId 
    union all 
    select c.PreviousID, c.CurrentID, c.Data, level = p.level +1 
    from t c 
    inner join cte as p 
     on c.PreviousID = p.CurrentID 
) 
insert into #temp 
select p.PreviousId, t.level, x.col, x.value 
    , rn = row_number() over (order by t.level, x.col) 
from cte t 
    cross apply (
    select top 1 
     PreviousId 
     from cte i 
     order by level 
    ) as p (PreviousId) 
    cross apply (
    values ('CurrentId',convert(varchar(32),CurrentId)),('Data',Data) 
    ) as x (col,value); 

效果爲止：

+------------+-------+-----------+--------+----+ 
| PreviousID | Level | Col | Value | rn | 
+------------+-------+-----------+--------+----+ 
|   2 |  0 | CurrentId | 3  | 1 | 
|   2 |  0 | Data  | Data 2 | 2 | 
|   2 |  1 | CurrentId | 4  | 3 | 
|   2 |  1 | Data  | Data 3 | 4 | 
|   2 |  2 | CurrentId | 5  | 5 | 
|   2 |  2 | Data  | Data 4 | 6 | 
+------------+-------+-----------+--------+----+ 

---

生成並執行動態SQL pivot()臨時表。

/* pivot */ 
declare @cols nvarchar(max); 
declare @sql nvarchar(max); 
select @cols = stuff((
    select 
     ', Col'+convert(nvarchar(10),rn) 
     from #temp 
     order by 1 
     for xml path (''), type).value('.','nvarchar(max)') 
    ,1,1,'') 
select @sql =' 
select Col0=PreviousID, ' + @cols +' 
    from (
    select PreviousID, Value, rn= ''Col''+convert(nvarchar(10),rn) 
     from #temp 
    ) as t 
pivot (max([Value]) for [rn] in (' + @cols +')) p' 
select @sql as CodeGenerated; 
exec sp_executesql @sql; 

代碼生成：

select Col0=PreviousID, Col1, Col2, Col3, Col4, Col5, Col6 
    from (
    select PreviousID, Value, rn= 'Col'+convert(nvarchar(10),rn) 
     from #temp 
    ) as t 
pivot (max([Value]) for [rn] in (Col1, Col2, Col3, Col4, Col5, Col6)) p 

回報：

+------+------+--------+------+--------+------+--------+ 
| Col0 | Col1 | Col2 | Col3 | Col4 | Col5 | Col6 | 
+------+------+--------+------+--------+------+--------+ 
| 2 | 3 | Data 2 | 4 | Data 3 | 5 | Data 4 | 
+------+------+--------+------+--------+------+--------+ 

---

（候補）生成並執行動態SQL使用條件聚合代替pivot()：產生

/* conditional aggregation */ 
--declare @cols nvarchar(max); 
--declare @sql nvarchar(max); 
select @cols = stuff((
    select 
     char(10)+'  , ' 
     + 'Col'+convert(nvarchar(10),rn) 
     +' = max(case when rn = '+convert(nvarchar(10),rn)+' then Value end)' 
    from #temp 
    order by 1 
    for xml path (''), type).value('.','nvarchar(max)') 
    ,1,0,'') 
select @sql =' 
select Col0 = PreviousID'+@cols+' 
from #temp 
group by PreviousID' 
select @sql as CodeGenerated; 
exec sp_executesql @sql; 

代碼：

select Col0 = PreviousID 
    , Col1 = max(case when rn = 1 then Value end) 
    , Col2 = max(case when rn = 2 then Value end) 
    , Col3 = max(case when rn = 3 then Value end) 
    , Col4 = max(case when rn = 4 then Value end) 
    , Col5 = max(case when rn = 5 then Value end) 
    , Col6 = max(case when rn = 6 then Value end) 
from #temp 
group by PreviousID 

回報：

+------+------+--------+------+--------+------+--------+ 
| Col0 | Col1 | Col2 | Col3 | Col4 | Col5 | Col6 | 
+------+------+--------+------+--------+------+--------+ 
| 2 | 3 | Data 2 | 4 | Data 3 | 5 | Data 4 | 
+------+------+--------+------+--------+------+--------+ 

Answer 2

我認爲嘗試連接列並給他們別名。 爲了更好地理解通過這個鏈接https://www.mssqltips.com/sqlservertip/2985/concatenate-sql-server-columns-into-a-string-with-concat/