巧用top percent優化top 1

廢話很少說，直接上sql

SELECT  top 1  B.CREW_ID, E.CREW_NAME,C.OFFBLK,C.ONBLK,dbo.PEK_OPS_Date(A.STD) as STD
          FROM dbo.FLIGHTS A 
        LEFT OUTER JOIN
          (SELECT DISTINCT TASK_ID, CREW_ID
           FROM dbo.CREW_TASK
          ) B ON A.COCKPIT_CREW_GROUP = B.TASK_ID 
        LEFT OUTER JOIN dbo.FLIGHTS_CREW_REPORT C ON A.FLTID = C.FLTID 
        LEFT JOIN CREW_INFO E ON B.CREW_ID = E.CREW_ID
        LEFT JOIN FLIGHTS_STC F ON A.STC = F.IATA_CODE
      WHERE (A.COCKPIT_CREW_GROUP > 0) AND (A.STATUS='ATA')
        AND F.RATIO = 1 AND NOT (A.AC LIKE '%--%')
        AND B.CREW_ID = ISNULL(60, B.CREW_ID) AND C.OFFBLK is not null AND C.ONBLK is not null
        AND  C.CREW_LEFT is not null AND C.CREW_RIGHT is not null 
     ORDER BY A.STD desc

執行計劃以下：

 

執行時間： 16秒、

 

分析：

嵌套循環以前，進行了排序操做，驅動表CREW_TASK 單表數據量300232。去重排序以後29w+。FLIGHTS 表單表44w+，這裏不走hash 的緣由是由於top1致使。故去掉 TOP 1 限制語句

 

SELECT   B.CREW_ID, E.CREW_NAME,C.OFFBLK,C.ONBLK,dbo.PEK_OPS_Date(A.STD) as STD
          FROM dbo.FLIGHTS A 
        LEFT OUTER JOIN
          (SELECT DISTINCT TASK_ID, CREW_ID
           FROM dbo.CREW_TASK
          ) B ON A.COCKPIT_CREW_GROUP = B.TASK_ID 
        LEFT OUTER JOIN dbo.FLIGHTS_CREW_REPORT C ON A.FLTID = C.FLTID 
        LEFT JOIN CREW_INFO E ON B.CREW_ID = E.CREW_ID
        LEFT JOIN FLIGHTS_STC F ON A.STC = F.IATA_CODE
      WHERE (A.COCKPIT_CREW_GROUP > 0) AND (A.STATUS='ATA')
        AND F.RATIO = 1 AND NOT (A.AC LIKE '%--%')
        AND B.CREW_ID = ISNULL(60, B.CREW_ID) AND C.OFFBLK is not null AND C.ONBLK is not null
        AND  C.CREW_LEFT is not null AND C.CREW_RIGHT is not null 
     ORDER BY A.STD desc

執行計劃：

 

執行時間：

分析：很明顯hash走了hash 匹配，可見在雙大表狀況下，hash 匹配返回5000多行比嵌套循環返回一條要快得多。

方向明確，那麼怎麼取上述第一條數據呢？這個時候用到 TOP percent，也就是返回結果集的一個比例值，而不是 top 1 第一條數據：

sql以下：

SELECT  top 100 percent B.CREW_ID, E.CREW_NAME,C.OFFBLK,C.ONBLK,dbo.PEK_OPS_Date(A.STD) as STD
          FROM dbo.FLIGHTS A 
        LEFT OUTER JOIN
          (SELECT DISTINCT TASK_ID, CREW_ID
           FROM dbo.CREW_TASK
          ) B ON A.COCKPIT_CREW_GROUP = B.TASK_ID 
        LEFT OUTER JOIN dbo.FLIGHTS_CREW_REPORT C ON A.FLTID = C.FLTID 
        LEFT JOIN CREW_INFO E ON B.CREW_ID = E.CREW_ID
        LEFT JOIN FLIGHTS_STC F ON A.STC = F.IATA_CODE
      WHERE (A.COCKPIT_CREW_GROUP > 0) AND (A.STATUS='ATA')
        AND F.RATIO = 1 AND NOT (A.AC LIKE '%--%')
        AND B.CREW_ID = ISNULL(60, B.CREW_ID) AND C.OFFBLK is not null AND C.ONBLK is not null
        AND  C.CREW_LEFT is not null AND C.CREW_RIGHT is not null 
     ORDER BY A.STD desc

執行時間 ，返回100%的結果集

 

怎麼返回第一條？很簡單，我返回1%的結果集以下：

 

 

SELECT  top 1 percent B.CREW_ID, E.CREW_NAME,C.OFFBLK,C.ONBLK,dbo.PEK_OPS_Date(A.STD) as STD
          FROM dbo.FLIGHTS A 
        LEFT OUTER JOIN
          (SELECT DISTINCT TASK_ID, CREW_ID
           FROM dbo.CREW_TASK
          ) B ON A.COCKPIT_CREW_GROUP = B.TASK_ID 
        LEFT OUTER JOIN dbo.FLIGHTS_CREW_REPORT C ON A.FLTID = C.FLTID 
        LEFT JOIN CREW_INFO E ON B.CREW_ID = E.CREW_ID
        LEFT JOIN FLIGHTS_STC F ON A.STC = F.IATA_CODE
      WHERE (A.COCKPIT_CREW_GROUP > 0) AND (A.STATUS='ATA')
        AND F.RATIO = 1 AND NOT (A.AC LIKE '%--%')
        AND B.CREW_ID = ISNULL(60, B.CREW_ID) AND C.OFFBLK is not null AND C.ONBLK is not null
        AND  C.CREW_LEFT is not null AND C.CREW_RIGHT is not null 
     ORDER BY A.STD desc

執行時間：，很明顯返回的是1%的結果集

返回0.01的結果集：

SELECT  top 0.01 percent B.CREW_ID, E.CREW_NAME,C.OFFBLK,C.ONBLK,dbo.PEK_OPS_Date(A.STD) as STD
          FROM dbo.FLIGHTS A 
        LEFT OUTER JOIN
          (SELECT DISTINCT TASK_ID, CREW_ID
           FROM dbo.CREW_TASK
          ) B ON A.COCKPIT_CREW_GROUP = B.TASK_ID 
        LEFT OUTER JOIN dbo.FLIGHTS_CREW_REPORT C ON A.FLTID = C.FLTID 
        LEFT JOIN CREW_INFO E ON B.CREW_ID = E.CREW_ID
        LEFT JOIN FLIGHTS_STC F ON A.STC = F.IATA_CODE
      WHERE (A.COCKPIT_CREW_GROUP > 0) AND (A.STATUS='ATA')
        AND F.RATIO = 1 AND NOT (A.AC LIKE '%--%')
        AND B.CREW_ID = ISNULL(60, B.CREW_ID) AND C.OFFBLK is not null AND C.ONBLK is not null
        AND  C.CREW_LEFT is not null AND C.CREW_RIGHT is not null 
     ORDER BY A.STD desc

執行時間：   已經達到要求。

 

注意：這裏返回的是結果集的 百分比，雖然如今知足取第一條的要求，可是是隨數據量增大，可能會多條， 故，外面包一層，取TOP 1 這樣能保證只取一條。

select top 1 AA.* from (
SELECT  top 1 percent B.CREW_ID, E.CREW_NAME,C.OFFBLK,C.ONBLK,dbo.PEK_OPS_Date(A.STD) as STD
          FROM dbo.FLIGHTS A 
        LEFT OUTER JOIN
          (SELECT DISTINCT TASK_ID, CREW_ID
           FROM dbo.CREW_TASK
          ) B ON A.COCKPIT_CREW_GROUP = B.TASK_ID 
        LEFT OUTER JOIN dbo.FLIGHTS_CREW_REPORT C ON A.FLTID = C.FLTID 
        LEFT JOIN CREW_INFO E ON B.CREW_ID = E.CREW_ID
        LEFT JOIN FLIGHTS_STC F ON A.STC = F.IATA_CODE
      WHERE (A.COCKPIT_CREW_GROUP > 0) AND (A.STATUS='ATA')
        AND F.RATIO = 1 AND NOT (A.AC LIKE '%--%')
        AND B.CREW_ID = ISNULL(60, B.CREW_ID) AND C.OFFBLK is not null AND C.ONBLK is not null
        AND  C.CREW_LEFT is not null AND C.CREW_RIGHT is not null 
     ORDER BY A.STD desc )AA

執行時間：

 

 

 

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