从存储为字符串的数字中提取分数

Question

I've got a field in this database that stores number like so:

• 80 1/4
• 20 1/8
• 20
• 36 15/16
• 44 1/8
• 93 7/8
• 89 1/8

I'm trying to convert these to a full decimal so I can add them up. I've been trying to do this by extracting the fraction out of the number, converting that to a decimal and then adding that to the whole number. I've been having some major problems extracting the numerator. The denominator has been extracted using:

CASE WHEN CHARINDEX('/',Fraction) > 0 THEN RIGHT(Faction,(LEN(Fraction) - (CHARINDEX('/',Fraction)))) ELSE NULL END AS [Denominator]

I'm not sure if that's the most efficient way to do it but it seems to work.

I've tried to pull the numerator out using this method:

CASE WHEN Charindex('/', Fraction) > 0 THEN LEFT(RIGHT(Fraction, Len(Fraction) - Charindex(' ',Fraction)), CHARINDEX('/',Fraction) - 1) ELSE NULL END AS [Numerator]

But that just gives me the fraction itself. I'm not sure if SQL has a problem with a RIGHT inside a LEFT since it doesn't seem to do anything, or, more likely, my code is messed up.

Anyone have any ideas?

Thanks!

Answer 1

You almost got it right: you are calculating the length that you pass to LEFT incorrectly. You need to take the position of space into account.

Instead of

CHARINDEX('/',Fraction) - 1

the length should be

CHARINDEX('/',Fraction) - CHARINDEX(' ',Fraction) - 1

The overall expression should look like this:

CASE WHEN Charindex('/', Fraction) > 0 THEN LEFT(RIGHT(Fraction, Len(Fraction) - Charindex(' ',Fraction)), CHARINDEX('/',Fraction) - CHARINDEX(' ',Fraction) - 1) ELSE NULL END AS [Numerator]

Link to demo on sqlfiddle.

Answer 2

This should work. I've moved the CHARINDEX functions to inside an APPLY just to try and make it more legible

WITH Data AS
(   SELECT  Fraction
    FROM    (VALUES
                ('80 1/4'),
                ('20 1/8'),
                ('20'),
                ('36 15/16'),
                ('44 1/8'),
                ('93 7/8'),
                ('89 1/8')
            ) t (Fraction)
), Workings AS
(   SELECT  Fraction,
            WholeNumber = CAST(CASE WHEN FractionIndex = 0 THEN Fraction ELSE LEFT(Fraction, SpaceIndex) END AS FLOAT),
            Numerator = CAST(CASE WHEN FractionIndex > 0 THEN SUBSTRING(Fraction, SpaceIndex, FractionIndex - SpaceIndex) END AS FLOAT),
            Demonimator = CAST(CASE WHEN FractionIndex > 0 THEN SUBSTRING(Fraction, FractionIndex + 1, LEN(Fraction)) END AS FLOAT)
    FROM    Data
            CROSS APPLY 
            (   SELECT  FractionIndex = CHARINDEX('/', Fraction),
                        SpaceIndex = CHARINDEX(' ', Fraction)
            ) f
)
SELECT  *,
        [Decimal] = CAST(WholeNumber + COALESCE(Numerator / Demonimator, 0) AS FLOAT)
FROM    Workings

Answer 3

Here is something you can try:

with t as (select '80 123/456' as val)
select (case when val like '% %/%'
             then cast(left(val, charindex(' ', val)) as float) +
                  (cast(SUBSTRING(val, charindex(' ', val), CHARINDEX('/', val) - charindex(' ', val)) as float) /
                   CAST(SUBSTRING(val, charindex('/', val)+1, 100) as int)
                  )
             else cast(val as float)
        end)
from t

Answer 4

Just copy replace the variable with your column name and place in the portion of your case statement where your "CHARINDEX('/',Fraction) > 0" is true.

Declare @num varchar(50) = '1004 1/3'

--      Numerator
Select  Left(Right(@num,Len(@num)-CharIndex(' ',@num)),CharIndex('/',Right(@num,Len(@num)-CharIndex(' ',@num)))-1)
--      Denominator
Select  Right(Right(@num,Len(@num)-CharIndex(' ',@num)),Len(Right(@num,Len(@num)-CharIndex(' ',@num)))-CharIndex('/',Right(@num,Len(@num)-CharIndex(' ',@num))))