Question

I am currently trying to split one value with percentage column. But as most of percentages values are 1/3, I am not able to get aboslute 100% with two decimal points in the value. For example:

Product    Supplier      percentage         totalvalue        customer_split
                         decimal(15,14)   (decimal(18,2)       decimal(18,2)
--------   --------     ------------     ---------------  ---------------
Product1    Supplier1    0.33            10.00                3.33
Product1    Supplier2    0.33            10.00                3.33
Product1    Supplier3    0.33            10.00                3.33

So, here we are missing 0.01 in the value column and suppliers would like to put this missing 0.01 value against any one of the supplier randomly. I have been trying to get this done in a two sets of SQLs with temporary tables, but is there any simple way of doing this. If possible how can I get 0.34 in the percentage column itself for one of the above rows? 0.01 is negligible value, but when the value column is 1000000000 it is significant.

Answer 1

It sounds like you’re doing some type of “allocation” here. This is a common problem any time you are trying to allocate something from a higher granulartiy to a lower granularity, and you need to be able to re-aggregate to the total value correctly.

This becomes a much bigger problem when dealing with larger fractions.

For example, if I try to divide a total value of, say $55.30 by eight, I get a decimal value of $6.9125 for each of the eight buckets. Should I round one to $6.92 and the rest to $6.91? If I do, I will lose a cent. I would have to round one to $6.93 and the others to $6.91. This gets worse as you add more buckets to divide by.

In addition, when you start to round, you introduce problems like “Should 33.339 be rounded to 33.34 or 33.33?”

If your business logic is such that you just want to take whatever remainder beyond 2 significant digits may exist and add it to one of the dollar values “randomly” so you don’t lose any cents, @Diego is on the right track with this.

Doing it in pure SQL is a bit more difficult. For starters, your percentage isn’t 1/3, it’s .33, which will yield a total value of 9.9, not 10. I would either store this as a ratio or as a high-precision decimal field (.33333333333333).

P    S    PCT           Total  
--   --   ------------  ------  
P1   S1   .33333333333  10.00   
P2   S2   .33333333333  10.00   
P3   S3   .33333333333  10.00   


SELECT 
   BaseTable.P, BaseTable.S, 
   CASE WHEN BaseTable.S = TotalTable.MinS 
      THEN BaseTable.BaseAllocatedValue + TotalTable.Remainder
      ELSE BaseTable.BaseAllocatedValue
   END As AllocatedValue
FROM
(SELECT
   P, S, FLOOR((PCT * Total * 100)) / 100 as BaseAllocatedValue,
   FROM dataTable) BaseTable
INNER JOIN
(SELECT
   P, MIN(S) AS MinS,
   SUM((PCT * Total) - FLOOR((PCT * Total * 100)) / 100) as Remainder,
FROM dataTable
GROUP BY P) as TotalTable
ON (BaseTable.P = TotalTable.P)

It appears your calculation is an equal distribution based on the total number of products per supplier. If it is, it may be advantageous to remove the percentage and instead just store the count of items per supplier in the table.

If it is also possible to store a flag indicating the row that should get the remainder value applied to it, you could assign based on that flag instead of randomly.