在刪除使用CTE不執行

Question

這裏是運行和運行原始查詢：

;WITH includedCs_cte 
    AS 
    (
    SELECT 
      x.PKey, 
      x.OKey, 
      y.CKey 
    FROM 
      #Permissions x 
      JOIN WHDATA.dbo.tb_DimC y 
        ON 
        x.PKey = y.PKey AND 
        x.OKey = y.OKey 
     ) 
, b_cte 
    AS 
    (
    SELECT 
      i.OKey, 
      i.PKey 
    FROM 
       WHData.dbo.vw_FactCX b 
       INNER JOIN includedCs_cte i 
         ON 
         b.PKey = i.PKey AND 
         b.PlayCKey = i.CKey 
    WHERE b.DateKey >= @myLAST28DAYS 
    GROUP BY 
      i.OKey, 
      i.PKey 
    ) 
, POK_cte 
    AS 
    (
    SELECT 
      i.OKey, 
      i.PKey 
    FROM 
       WHData.dbo.vw_FactCY b 
       INNER JOIN includedCs_cte i 
         ON 
         b.PKey = i.PKey AND 
         b.PlayCKey = i.CKey 
    WHERE b.DateKey >= @myLAST28DAYS 
    GROUP BY 
      i.OKey, 
      i.PKey 
    ) 
, includedOKeys 
    AS 
    (
    SELECT * 
    FROM b_cte 
    UNION 
    SELECT * FROM POK_cte 
    ) 
DELETE FROM #Permissions 
FROM #Permissions p 
WHERE NOT EXISTS 
        (
        SELECT 1 
        FROM includedOKeys x 
        WHERE 
          p.PKey = x.PKey AND 
          p.OKey = x.OKey  
        ) 

如果更改以上至低於然後在不到10秒的運行。爲什麼這些執行如此不同？

;WITH includedCs_cte 
    AS 
    (
    SELECT 
      x.PKey, 
      x.OKey, 
      y.CKey 
    FROM 
      #Permissions x 
      JOIN WHDATA.dbo.tb_DimC y 
        ON 
        x.PKey = y.PKey AND 
        x.OKey = y.OKey 
     ) 
, b_cte 
    AS 
    (
    SELECT 
      i.OKey, 
      i.PKey 
    FROM 
       WHData.dbo.vw_FactCX b 
       INNER JOIN includedCs_cte i 
         ON 
         b.PKey = i.PKey AND 
         b.PlayCKey = i.CKey 
    WHERE b.DateKey >= @myLAST28DAYS 
    GROUP BY 
      i.OKey, 
      i.PKey 
    ) 
, POK_cte 
    AS 
    (
    SELECT 
      i.OKey, 
      i.PKey 
    FROM 
       WHData.dbo.vw_FactCY b 
       INNER JOIN includedCs_cte i 
         ON 
         b.PKey = i.PKey AND 
         b.PlayCKey = i.CKey 
    WHERE b.DateKey >= @myLAST28DAYS 
    GROUP BY 
      i.OKey, 
      i.PKey 
    ) 
, includedOKeys 
    AS 
    (
    SELECT * 
    FROM b_cte 
    UNION 
    SELECT * FROM POK_cte 
    ) 
SELECT * 
INTO #includedOKeys 
FROM includedOKeys 
CREATE CLUSTERED INDEX ix_inclProdOper ON #includedOKeys(OKey, PKey) 

DELETE FROM #Permissions 
FROM #Permissions p 
WHERE NOT EXISTS 
     (
     SELECT 1 
     FROM #includedOKeys x 
     WHERE 
      p.PKey = x.PKey AND 
      p.OKey = x.OKey  
     ) 

Answer 1

CTE在使用時解決。這意味着如果您在查詢中使用它兩次，它可能會解決兩次。 CTE做並不總是得到解決一次並緩存在內存中。 SQL Server可以自由地執行查詢，因爲它認爲合適。

就你而言，它可能比這更糟 - 因爲你已經在EXISTS子句中使用它作爲相關的子查詢，這是一個逐行操作。這可能意味着計劃結果在CTE被解決了#permissions表的EACH ROW！那很可能是所有時間都會去的地方。在SSMS中顯示執行計劃（Ctrl-L）是你的朋友。

檢查此SQLFiddle，這表明沒有任何GUID是相同的，即使CTE只創建3行。事實上，我們得到18個不同的GUID。

with cte(guid,other) as (
    select newid(),1 union all 
    select newid(),2 union all 
    select newid(),3) 
select a.guid, a.other, b.guid guidb, b.other otherb 
from cte a 
cross join cte b 
order by a.other, b.other;