Convert fractional string to decimal - sql

Question

I've got a few columns that have values either in fractional strings (i.e. 6 11/32) or as decimals (1.5). Is there a CAST or CONVERT call that can convert these to consistently be decimals?
The error:
Msg 8114, Level 16, State 5, Line 1
Error converting data type varchar to numeric.
Can I avoid doing any kind of parsing?
Thanks!
P.S. I'm working in SQL Server Management Studio 2012.

Answer 1

CREATE FUNCTION ufn_ConvertToNumber(#STR VARCHAR(50))
RETURNS decimal(18,10)
AS
BEGIN
DECLARE #L VARCHAR(50) = ''
DECLARE #A DECIMAL(18,10) = 0
SET #STR = LTRIM(RTRIM(#STR)); -- Remove extra spaces
IF ISNUMERIC(#STR) > 0 SET #A = CONVERT(DECIMAL(18,10), #STR) -- Check to see if already real number
IF CHARINDEX(' ',#STR,0) > 0
BEGIN
SET #L = SUBSTRING(#STR,1,CHARINDEX(' ',#STR,0) - 1 )
SET #STR = SUBSTRING(#STR,CHARINDEX(' ',#STR,0) + 1 ,50 )
SET #A = CONVERT(DECIMAL(18,10), #L)
END
IF CHARINDEX('/',#STR,0) > 0
BEGIN
SET #L = SUBSTRING(#STR,1,CHARINDEX('/',#STR,0) - 1 )
SET #STR = SUBSTRING(#STR,CHARINDEX('/',#STR,0) + 1 ,50 )
SET #A = #A + ( CONVERT(DECIMAL(18,10), #L) / CONVERT(DECIMAL(18,10), #STR) )
END
RETURN #A
END
GO
Then access it via select dbo.ufn_ConvertToNumber ('5 9/5')

Answer 2

You'll need to parse. As Niels says, it's not really a good idea; but it can be done fairly simply with a T-SQL scalar function.
CREATE FUNCTION dbo.FracToDec ( #frac VARCHAR(100) )
RETURNS DECIMAL(14, 6)
AS
BEGIN
RETURN CASE
WHEN #frac LIKE '% %/%'
THEN CAST(LEFT(#frac, CHARINDEX(' ', #frac, 1) -1) AS DECIMAL(14,6)) +
( CAST(SUBSTRING(#frac, CHARINDEX(' ', #frac, 1) + 1, CHARINDEX('/', #frac, 1)-CHARINDEX(' ',#frac,1)-1) AS DECIMAL(14,6))
/ CAST(RIGHT(#frac, LEN(#frac) - CHARINDEX('/', #frac, 1)) AS DECIMAL(14,6)) )
WHEN #frac LIKE '%/%'
THEN CAST(LEFT(#frac, CHARINDEX('/', #frac, 1) - 1) AS DECIMAL(14,6)) / CAST(RIGHT(#frac, LEN(#frac) - CHARINDEX('/', #frac, 1)) AS DECIMAL(14,6))
ELSE
CAST(#frac AS DECIMAL(14,6))
END
END
GO
-- Test cases
SELECT dbo.FracToDec('22/7'), dbo.fracToDec('3.117'), dbo.fracToDec('7 3/4')
-- Output
-- 3.142857 3.117000 7.750000
Note that this will fail if the contents passed does not actually match the forms "mm/nn", "xx mm/nn" or a real decimal.

Answer 3

And here is the solution without functions and stored procedures - just for the fun of it. First you have to create new column (I call it decimal) and then fill it with the values converted from the original mixed-format column (called inconsistent) using the following query:
UPDATE "my_table"
SET "decimals" = CASE WHEN CHARINDEX('/', "inconsistent") > 0
THEN CAST(CASE WHEN CHARINDEX(' ',
RTRIM(LTRIM("inconsistent"))) > 0
THEN LEFT(RTRIM(LTRIM("inconsistent")),
CHARINDEX(' ',
RTRIM(LTRIM("inconsistent")))
- 1)
ELSE '0'
END AS FLOAT)
+ CAST(SUBSTRING(RTRIM(LTRIM("inconsistent")),
CHARINDEX(' ',
RTRIM(LTRIM("inconsistent")))
+ 1,
CHARINDEX('/',
RTRIM(LTRIM("inconsistent")))
- 1 - CHARINDEX(' ',
RTRIM(LTRIM("inconsistent")))) AS FLOAT)
/ CAST(RIGHT(RTRIM(LTRIM("inconsistent")),
LEN(RTRIM(LTRIM("inconsistent")))
- CHARINDEX('/',
RTRIM(LTRIM("inconsistent")))) AS FLOAT)
ELSE CAST(RTRIM(LTRIM("inconsistent")) AS FLOAT)
END

Answer 4

I am not aware of any database system, or code framework for that matter, supporting strings like 6 11/32 natively. Your best bet is to add a column to the relevant table and denormalize the actual value in there with a script, or creating a view on top of it that does that automatically. It'll take some complex code though, and it's probably not a good idea to do it in SQL at all.