SQL custom unit conversion

Question

I am looking for a solution for a custom unit conversion in SQL, the database my company used is Microsoft SQL server, I need to write a SQL to return a conversion factor based

Answer 1

I think a recursive table that finds a path from your desired from unit and to the desired to unit would work best. Something like this (This assumes that if there is a path a-->b-->c there is also a path c-->b-->a in the database. If not it could be modified to search both directions).

select  1001 as itemID
        ,5000 as vendorID
        ,10 as fromUnit
        ,500 as toUnit
        ,cast(1000 as float) as fromQuantity
        ,cast(1 as float) as toQuantity
into #conversionTable
union
select  1001
        ,5000
        ,500
        ,305
        ,1
        ,5
union
select 1001
        ,5000
        ,305
        ,500
        ,5
        ,1
union
select  1001
        ,5000
        ,500
        ,10
        ,1
        ,1000

declare @fromUnit int
        ,@toUnit int
        ,@input int
set @fromUnit = 305 --box
set @toUnit =  10 --gram
set @input = 10

;with recursiveTable as
(
    select  0 as LevelNum
            ,ct.fromUnit
            ,ct.toUnit
            ,ct.toQuantity / ct.fromQuantity as multiplicationFactor
    from #conversionTable ct
    where   ct.fromUnit = @fromUnit

    union all

    select  LevelNum + 1
            ,rt.fromUnit
            ,ct.toUnit
            ,rt.multiplicationFactor * (ct.toQuantity / ct.fromQuantity)
    from #conversionTable ct
    inner join recursiveTable rt on rt.toUnit = ct.fromUnit
)

select @input * r.multiplicationFactor
from
(
    select top 1 * from recursiveTable 
    where (fromUnit = @fromUnit
    and toUnit = @toUnit)
) r