sql server - mssql convert varchar to float

Question

I have a field value productlength of 0.123. This is from a view and has a data type of varchar.

I need to convert it to a float or numeric value so as o perform math comparisons.

convert(float,productlength) and cast(productlength as float) both do not work.

error varchar cant be converted to float or somethiing liek that.

From what I have read varchar can simply not be converted to a numeric string?

Any clever ways around this?

Answer 1

You can convert varchars to floats, and you can do it in the manner you have expressed. Your varchar must not be a numeric value. There must be something else in it. You can use IsNumeric to test it. See this:

declare @thing varchar(100)

select @thing = '122.332'

--This returns 1 since it is numeric.
select isnumeric(@thing)

--This converts just fine.
select convert(float,@thing)

select @thing = '122.332.'

--This returns 0 since it is not numeric.
select isnumeric(@thing)

--This convert throws.
select convert(float,@thing)