On Monday, January 7, 2013 3:27:58 PM UTC-8, Sean Mackesey wrote:
>
> I have a database entry (with model class `Number`) that I can't seem to
> match against. It has a field called "value", and the value appears to be
> 5.1. But I can't seem to match it via Sequel's `first` and `where`
> methods. There are other entries in the table that I have no trouble
> matching by the `value` field. What's going on?
>
> [37] pry(#<CountInference::Optimization::NumMarkerLoader>)> Number[17]
> => #<Number @values={:id=>17, :raw=>"5.1p#CA1:SR:do/CCK+#CB+",
> :value=>5.1, :std=>0.0, :type=>""}>
> [38] pry(#<CountInference::Optimization::NumMarkerLoader>)>
> Number[17].value
> => 5.1
> [39] pry(#<CountInference::Optimization::NumMarkerLoader>)>
> Number[17].value == 5.1
> => true
> [40] pry(#<CountInference::Optimization::NumMarkerLoader>)>
> Number.first(value: 5.1)
> => nil
> [42] pry(#<CountInference::Optimization::NumMarkerLoader>)>
> Number.where(value: 5.1).all
> => []
>
The value column is probably floating point (real or double precision
database type). You should not use equality when dealing with floating
point numbers, in ruby, SQL, or any other programming language. If you
don't understand how to use floating point numbers, Google should be able
to help you.
Try something like:
Number.where(value: (5.09999999999)..(5.100000000001)).all
Alternatively, if you want to use equality and can change the database
type, switch to a decimal/numeric type instead of a floating point type.
Thanks,
Jeremy
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