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My CTE is Producing Spurious Results

    질문

  • Hello experts!  I am trying to compare two fields named 'Reportable_Amount' in two tables.  I am joining on ID and AsOfDate.  I am getting differences between these two Reportable_Amount fields, in the CTE, but when I query each one separately, I can see there are really no differences, or at least I haven't found any differences when the CTE says there are differences.  Here is my T-SQL.

    WITH 
    cte1 AS (SELECT agg_boc_id, AsofDate, SUM(Reportable_Amount) AS Reportable_AMT
    FROM      TBL_FR2052A_AGG_BOC_HIST AS AGG
    GROUP BY   agg_boc_id, AsofDate), 
    cte2 AS
    (SELECT   AggBOCID, AsofDate, REPORTABLE_AMOUNT
    FROM      TBL_FR2052A_RAW_DATA_HIST)
    SELECT    cte2.AggBOCID, cte2.AsofDate, SUM(cte1.Reportable_AMT - cte2.REPORTABLE_AMOUNT) AS Amount
    FROM      cte1 AS cte1 INNER JOIN cte2 AS cte2
    		ON cte1.agg_boc_id = cte2.AggBOCID 
    		AND cte1.AsofDate = cte2.AsofDate
    GROUP BY cte1.agg_boc_id, cte1.AsofDate, cte2.AggBOCID, cte2.AsofDate
    HAVING (SUM(ROUND(cte1.Reportable_AMT, 0) - ROUND(cte2.REPORTABLE_AMOUNT, 0)) <> 0)

    What am I missing here?  Thanks.


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    2018년 6월 13일 수요일 오후 9:04

모든 응답

  • Hi,

    When you say you compare the two tables manually, are you also using the ROUND() function? I was just curious if the differences were due to some rounding errors/discrepancies.

    Just my 2 cents...


    • 편집됨 .theDBguyMVP 2018년 6월 13일 수요일 오후 9:46
    2018년 6월 13일 수요일 오후 9:16
  • You are missing GROUP BY from the second CTE.

    On the other hand, you do need any GROUP BY or SUM in the final SELECT.

    Right now you are comparing the SUM from cte1 with each invidual row in TBL_FR2052A_RAW_DATA_HIST which is unlikely to be useful.

    2018년 6월 13일 수요일 오후 9:44
  • Hi,

    As you said that there're differences when you run the queries separately. What're the differences? Could you please share us some sample about the differences?

    And if the differences are decimal part of Reportable_Amount value. Then I think your issue can be related to the ROUND() function. You should know that when the length parameter for ROUND() set to 0, the value will be rounded to the number of decimal positions specified by length and returned as a integer. For example, ROUND(312.269,0) = ROUND(312.123,0). Please check following sample:

    drop table #TBL_FR2052A_AGG_BOC_HIST,#TBL_FR2052A_RAW_DATA_HIST
    
    create table #TBL_FR2052A_AGG_BOC_HIST
    (
    agg_boc_id int,
    AsofDate date,
    Reportable_Amount float
    )
    
    insert into #TBL_FR2052A_AGG_BOC_HIST values
    (1,'2018-01-01',123.123),
    (1,'2018-01-01',123.456),
    (2,'2018-02-01',221.123),
    (2,'2018-02-01',111.324),
    (3,'2018-03-01',312.269)
    
    create table #TBL_FR2052A_RAW_DATA_HIST
    (
    AggBOCID int,
    AsofDate date,
    REPORTABLE_AMOUNT float
    )
    
    insert into #TBL_FR2052A_RAW_DATA_HIST values
    (1,'2018-01-01',246.579),
    (2,'2018-02-01',332.447),
    (3,'2018-03-01',312.123)
    
    ;WITH 
    cte1 AS (SELECT agg_boc_id, AsofDate, SUM(Reportable_Amount) AS Reportable_AMT
    FROM      #TBL_FR2052A_AGG_BOC_HIST AS AGG
    GROUP BY   agg_boc_id, AsofDate), 
    cte2 AS
    (SELECT   AggBOCID, AsofDate, REPORTABLE_AMOUNT
    FROM      #TBL_FR2052A_RAW_DATA_HIST)
    
    
    SELECT    cte2.AggBOCID, cte2.AsofDate, SUM(cte1.Reportable_AMT - cte2.REPORTABLE_AMOUNT) AS Amount
    FROM      cte1 AS cte1 INNER JOIN cte2 AS cte2
    		ON cte1.agg_boc_id = cte2.AggBOCID 
    		AND cte1.AsofDate = cte2.AsofDate
    GROUP BY cte1.agg_boc_id, cte1.AsofDate, cte2.AggBOCID, cte2.AsofDate
    HAVING (SUM(ROUND(cte1.Reportable_AMT, 0) - ROUND(cte2.REPORTABLE_AMOUNT, 0)) <> 0)

    Thanks,
    Xi Jin.


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    2018년 6월 14일 목요일 오전 2:45
  • Very hard to understand the issue as we dont have any idea on your tables as well as how they are related

    Visibly the difference seems to be in grouping. While cte1 is grouped on agg_boc_id, AsofDate

    , cte2 doesnt have any groups. This can cause problems in join if TBL_FR2052A_RAW_DATA_HIST

    has multiple entries for the agg_boc_id, AsofDate combination



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    2018년 6월 14일 목요일 오전 6:00
  • Hi ryguy72,

    What is the data type for the field 'Reportable_Amount'? If it is float, then that could be the reason. Float values are approximate and may return inconsistent values when aggregated. Learn more about this problem here: https://blogs.msdn.microsoft.com/qingsongyao/2009/11/14/query-on-float-datatype-may-return-inconsistent-result/

    To work around this problem you can use  convert the float values to decimal to get consistent results like below: 

    sum(cast(Reportable_Amount as decimal(30,4))) to get consistent result


    HTH,
    Cheers!!
    Ashish
    Please mark it as Answered if it answered your question or mark it as Helpful if it helped you solve your problem.

    2018년 6월 14일 목요일 오후 2:07