Nested Case Statement Syntax

I am trying to write a nested case statement to look back at the 3 prior months and give me an average. But I keep getting an error. Where am I wrong?



CASE
        WHEN LatestMonthNum=2
        THEN
            CASE
              WHEN MONTH(TodayDate)=1 and YEAR(TodayDate)=LatestYearNum or
              MONTH(TodayDate)=12 and YEAR(TodayDate)=LatestYearNum -1 or
              MONTH(TodayDate)=11 and YEAR(TodayDate)=LatestYearNum -1
               THEN ConvertedQuantity/3
             ELSE CASE WHEN LatestMonthNum=1 THEN
               CASE WHEN MONTH(TodayDate)=12 and YEAR(TodayDate)=LatestYearNum-1 or
              MONTH(TodayDate)=11 and YEAR(TodayDate)=LatestYearNum -1 or
              MONTH(TodayDate)=10 and YEAR(TodayDate)=LatestYearNum -1
               THEN ConvertedQuantity/3
              ELSE CASE WHEN MONTH(TodayDate)= LatestMonthNum-1 and YEAR(TodayDate)=LatestYearNum or MONTH(TodayDate)= LatestMonthNum-2 and YEAR(TodayDate)=LatestYearNum or MONTH(TodayDate)= LatestMonthNum-3 and YEAR(TodayDate)=LatestYearNum
             then ConvertedQuantity/3
             else null
           
             END as 'ThreeMoAvg'
nirajkrishnaAsked:
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Kent OlsenConnect With a Mentor Data Warehouse Architect / DBACommented:
Every CASE clause must have a matching END.  The indented code above shows that a few well placed END statements are needed.  I think that you want something like this, but it's hard to know.  Keep in mind that if a CASE statement doesn't find a match, NULL is returned so this may take some more work.

CASE WHEN LatestMonthNum=2
     THEN CASE WHEN MONTH(TodayDate)=1 and YEAR(TodayDate)=LatestYearNum or
                    MONTH(TodayDate)=12 and YEAR(TodayDate)=LatestYearNum -1 or
                    MONTH(TodayDate)=11 and YEAR(TodayDate)=LatestYearNum -1
               THEN ConvertedQuantity/3
          END
     ELSE CASE WHEN LatestMonthNum=1 
               THEN CASE WHEN MONTH(TodayDate)=12 and YEAR(TodayDate)=LatestYearNum-1 or
                              MONTH(TodayDate)=11 and YEAR(TodayDate)=LatestYearNum -1 or
                              MONTH(TodayDate)=10 and YEAR(TodayDate)=LatestYearNum -1
                         THEN ConvertedQuantity/3
                    END
          END
     ELSE CASE WHEN MONTH(TodayDate)= LatestMonthNum-1 and YEAR(TodayDate)=LatestYearNum or
                    MONTH(TodayDate)= LatestMonthNum-2 and YEAR(TodayDate)=LatestYearNum or 
                    MONTH(TodayDate)= LatestMonthNum-3 and YEAR(TodayDate)=LatestYearNum
               then ConvertedQuantity/3
               else null
          END
END as 'ThreeMoAvg' 

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Kent OlsenData Warehouse Architect / DBACommented:
Howdy...

Indenting the code makes it really easy to see.  :)

CASE WHEN LatestMonthNum=2
     THEN CASE WHEN MONTH(TodayDate)=1 and YEAR(TodayDate)=LatestYearNum or
                    MONTH(TodayDate)=12 and YEAR(TodayDate)=LatestYearNum -1 or
                    MONTH(TodayDate)=11 and YEAR(TodayDate)=LatestYearNum -1
               THEN ConvertedQuantity/3
               ELSE CASE WHEN LatestMonthNum=1 
                         THEN CASE WHEN MONTH(TodayDate)=12 and YEAR(TodayDate)=LatestYearNum-1 or
                                        MONTH(TodayDate)=11 and YEAR(TodayDate)=LatestYearNum -1 or
                                        MONTH(TodayDate)=10 and YEAR(TodayDate)=LatestYearNum -1
                                   THEN ConvertedQuantity/3
                                   ELSE CASE WHEN MONTH(TodayDate)= LatestMonthNum-1 and YEAR(TodayDate)=LatestYearNum or
                                                  MONTH(TodayDate)= LatestMonthNum-2 and YEAR(TodayDate)=LatestYearNum or 
                                                  MONTH(TodayDate)= LatestMonthNum-3 and YEAR(TodayDate)=LatestYearNum
                                             then ConvertedQuantity/3
                                             else null
                                   END as 'ThreeMoAvg' 

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It's really tough to see what you're trying to achieve.  Can you explain it?  The SQL should be easy.  :)


Kent
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Jim HornMicrosoft SQL Server Developer, Architect, and AuthorCommented:
<knee-jerk reaction>
I see AND and OR in the same clauses, but no parentheses ( ) to determine order of execution.  

I'm guessing the first block should be this:

CASE WHEN
    (MONTH(TodayDate)=1 and YEAR(TodayDate)=LatestYearNum) or
    (MONTH(TodayDate)=12 and YEAR(TodayDate)=LatestYearNum -1) or
    (MONTH(TodayDate)=11 and YEAR(TodayDate)=LatestYearNum -1)
      THEN ConvertedQuantity/3

Without the parentheses ( ), it's going to do each and .. or ... and as an entire set, and since Month(TodayDate) is likely a single value per row, it'll never evaluate as True and return the THEN expression, only the ELSE expression.
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nirajkrishnaAuthor Commented:
This is just the calculated column and not the whole query. I am cross joined to a single row table that gives me the most recent date and  latest month number (LatestMonthNum) and latest year (LatestYearNum)
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nirajkrishnaAuthor Commented:
I am trying to say if the LatestMonthNum = 2 or 1 which means Jan or Feb then look at the latest month number and use the appropriate 3 prior months totals divided by 3 to give me an average. If it is not Jan or Feb then look at the data and when the month falls into the 3 prior months of today then add it to this column and divide it by 3 otherwise leave blank.


I am making a quick daily report that shows the current months performance (convertedQuantity) vs last month vs 3 prior month average.
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gplanaCommented:
as kdo said, every case should finish with an end. Try to change your expression by the expression added by kdo
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Kent OlsenData Warehouse Architect / DBACommented:
All that this complicated CASE statement does is divide ConvertedQuantity by 3.  Or not.

You probably want record selection (the WHERE filter) to determine which rows to process and just divide by 3.
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nirajkrishnaAuthor Commented:
This worked perfectly except for at the end I had to add one more "END" before the "END AS". Thanks!
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