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Banker's Rounding

Posted on 2004-10-03
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Last Modified: 2008-02-01
MS SQL Server has the Round function that rounds-off of mid-values (0.5, 5, 50, 500, etc.) up. Is there a function that will round-off mid-values according to Banker's Rounding, which will round of mid-values always to the even value? Anyone has one?
0.5->0
1.5->2
2.5->2
3.5->4
Thanks! :)
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Accepted Solution

by:
tomcat75 earned 43 total points
ID: 12214982
this is for Oracle
but for MSSQL  use the same logic (usinga i think CASE ...)

DECODE(VAR-ROUND(VAR,0),-0.5,DECODE(FLOOR(VAR)/2, FLOOR(FLOOR(VAR)/2),FLOOR(VAR),ROUND(VAR,0)),ROUND(VAR,0))

HTH
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Expert Comment

by:tomcat75
ID: 12215003
maybe an explanation will help

if
VAR-ROUND(VAR,0)=-0.5 (for 0.5 fractions)
if
FLOOR(VAR)/2=FLOOR(FLOOR(VAR)/2) --the number is even
then
FLOOR(VAR),
else
ROUND(VAR,0,
endif
ROUND(VAR,0)
endif


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Assisted Solution

by:kemp_a
kemp_a earned 41 total points
ID: 12215025
Hmm, funny, most MS development products used Bankers Rounding, some of the applications like Excel dont, but thats another story.

You can emulate Banker Rounding using the following formula:

round((Value*100-Half of the rounding value)/100)

eg

round(12.5*100-0.05)/100=12 or

Cheers
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Assisted Solution

by:xabimond
xabimond earned 41 total points
ID: 12215706
Encapsulated in a searched case:

declare @d as decimal(10,2)
set @d = 1.5
print @d

select (case when @d - round(@d, 0) <> -.5 then round(@d, 0)
      when (convert(int, floor(@d)) % 2) = 0 then floor(@d)
      else ceiling(@d)
      end) banker_rounded_number

Replace @d with your field name if appropriate.
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Author Comment

by:dabestprogrammerindauniverse
ID: 12336432
i will try your solutions out and will then award my points :)
thanks to everyone.
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Expert Comment

by:Alan Warren
ID: 12441471
Hi dabestprogrammerindauniverse,

This function will round up or down to the degree you specify.

-- Round up to the the nearest cent
-- Set @Somevarmoney = dbo.RoundToNearest(@SomeVarmoney,.01,1)

-- Round down to the the nearest cent
-- Set @Somevarmoney = dbo.RoundToNearest(@SomeVarmoney,.01,0)


CREATE Function [dbo].[RoundToNearest] (@Amt decimal(38, 19), @RoundAmt decimal(38, 19), @Direction bit)
-- @Direction=1 for RoundUp, @Direction=0 for RoundDown
RETURNS decimal(38, 19) AS  
BEGIN
  RETURN (CASE WHEN CONVERT(BIGINT, @Amt/@RoundAmt)=@Amt/@RoundAmt THEN @Amt ELSE (CONVERT(BIGINT, @Amt/@RoundAmt)+@Direction)*@RoundAmt END)
END


Alan
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Expert Comment

by:kemp_a
ID: 12748030
May I ask the reason for this recommendation.

Not discounting alanwarren's solution, which appears in essence very similar to the three previously posted solutions albeit posted 25 days after those solutions, and indeed 11 days after the asker posted they would try the already proffered solutions.

I believe the point should be shared between Tomcat75, xabimond & myself as these were posted prior to the askers final post and indeed in good hast to the askers question.

I look forward to your reply.
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