CTE SQL Server查詢的性能問題

Question

我們有一個具有父子關係的表，表示深層樹結構。

我們正在使用CTE查看數據，但性能較差（請參閱下面的代碼和執行計劃）。

有沒有什麼辦法可以提高性能？

WITH cte (ParentJobTypeId, Id) AS 
( 
    SELECT 
     Id, Id 
    FROM  
     dbo.JobTypes 

    UNION ALL 

    SELECT 
     e.Id, cte.Id 
    FROM  
     cte 
    INNER JOIN 
     dbo.JobTypes AS e ON e.ParentJobTypeId = cte.ParentJobTypeId 
) 
SELECT 
    ISNULL(Id, 0) AS ParentJobTypeId, 
    ISNULL(ParentJobTypeId, 0) AS Id 
FROM  
    cte 

Answer 1

使用範圍的鍵的一個簡單的例子。正如我前面提到的，等級分別爲127K點和一些部分，其中深15級

CTE的構建，讓我們假設票數結果將被存儲在一個表中（索引爲好）

Declare @Table table(ID int,ParentID int,[Status] varchar(50)) 
Insert @Table values 
(1,101,'Pending'), 
(2,101,'Complete'), 
(3,101,'Complete'), 
(4,102,'Complete'), 
(101,null,null), 
(102,null,null) 


;With cteOH (ID,ParentID,Lvl,Seq) 
as (
    Select ID,ParentID,Lvl=1,cast(Format(ID,'000000') + '/' as varchar(500)) from @Table where ParentID is null 
    Union All 
    Select h.ID,h.ParentID,cteOH.Lvl+1,Seq=cast(cteOH.Seq + Format(h.ID,'000000') + '/' as varchar(500)) From @Table h INNER JOIN cteOH ON h.ParentID = cteOH.ID 
    ), 
    cteR1 as (Select ID,Seq,R1=Row_Number() over (Order by Seq) From cteOH), 
    cteR2 as (Select A.ID,R2 = max(B.R1) From cteOH A Join cteR1 B on (B.Seq Like A.Seq+'%') Group By A.ID) 
    Select B.R1 
      ,C.R2 
      ,A.Lvl 
      ,A.ID 
      ,A.ParentID 
    Into #TempHier 
    From cteOH A 
    Join cteR1 B on (A.ID=B.ID) 
    Join cteR2 C on (A.ID=C.ID) 

    Select * from #TempHier 

    Select H.R1 
      ,H.R2 
      ,H.Lvl 
      ,H.ID 
      ,H.ParentID 
      ,Total = count(*) 
      ,Complete = sum(case when D.Status = 'Complete' then 1 else 0 end) 
      ,Pending = sum(case when D.Status = 'Pending' then 1 else 0 end) 
      ,PctCmpl = format(sum(case when D.Status = 'Complete' then 1.0 else 0.0 end)/count(*),'##0.00%') 
    From #TempHier H 
    Join (Select _R1=B.R1,A.* From @Table A Join #TempHier B on A.ID=B.ID) D on D._R1 between H.R1 and H.R2 
    Group By H.R1 
      ,H.R2 
      ,H.Lvl 
      ,H.ID 
      ,H.ParentID 
    Order By 1 

返回現在在#Temp表中的更高層。注意R1和R2，我稱這些爲範圍鍵。數據（沒有遞歸）可以通過這些鍵

R1 R2 Lvl ID ParentID 
1 4 1 101 NULL 
2 2 2 1 101 
3 3 2 2 101 
4 4 2 3 101 
5 6 1 102 NULL 
6 6 2 4 102 

非常簡單的例子來選擇和聚合：說明了滾動數據向上票數。

R1 R2 Lvl ID ParentID Total Complete Pending PctCmpl 
1 4 1 101 NULL  4  2   1  50.00% 
2 2 2 1 101   1  0   1  0.00% 
3 3 2 2 101   1  1   0  100.00% 
4 4 2 3 101   1  1   0  100.00% 
5 6 1 102 NULL  2  1   0  50.00% 
6 6 2 4 102   1  1   0  100.00% 

的範圍按鍵的真正的美，是如果你知道一個ID，你知道它的存在（所有後代和祖先）。