Home/ Questions/Q 6929359
In Process

The Archive Base Latest Questions

Editorial Team
  • 0
Asked: 2026-05-27T11:18:25+00:00

I have table with float column (I’m using MySQL, mysql2 gem, everything standard) create_table

  • 0

I have table with float column (I’m using MySQL, mysql2 gem, everything standard)

create_table :some_table do |t| 
  t.float  :amount 
end

I was playing around in console, when i do 

a = SomeTable.new
a.amount = 9999.99
a.save!
#9999.99
a.amount
#9999.99
a.reload
a.amount
#9999.99

everything ok 

a = SomeTable.new
a.amount = 9999.999
a.save!
#9999.999
a.amount 
#9999.999
a.reload
a.amount
#10000.00

as you see ruby (or rails ) rounds the numbers.

Can someone explain me why is that? …or is just me ?

Share

Leave an answer

You must login to add an answer.

Need An Account,

1 Answer

  1. Editorial Team

    If you want to know all about floats and why they have rounding errors, see What Every Computer Scientist Should Know About Floating-Point Arithmetic.

    If you are tying to do currency calculations, don’t use float! Use a fixed point data type.
    If you use rails migrations, the decimal type is what you want as described here.

    • 0