On Fri, Aug 19, 2011 at 16:09, Henry House
On Friday, 19 August 2011, Erik Hesselink wrote:
Do you really need the precision info about the column, or do you just need the values at the right precision? Because you get the last thing already:
Prelude Database.HDBC.PostgreSQL Database.HDBC Data.Ratio Control.Monad> (fromSql . head . head) `liftM` (quickQuery db "select 1.231 ::numeric(5,0);" []) :: IO Rational 1 % 1 Prelude Database.HDBC.PostgreSQL Database.HDBC Data.Ratio Control.Monad> (fromSql . head . head) `liftM` (quickQuery db "select 1.231 ::numeric(5,4);" []) :: IO Rational 1231 % 1000
I'm not sure I understand the distinction --- to my way of thinking, getting the value at the right precision means getting the correct number of significant decimal digits, which both your example and mine fail to provide.
Prelude Database.HDBC.PostgreSQL Database.HDBC Data.Ratio Control.Monad> (fromSql . head . head) `liftM` (quickQuery db "select 1.231 ::numeric(10,4);" []) :: IO Rational -- gives 1231 % 1000 == 1.231 in decimal notation Prelude Database.HDBC.PostgreSQL Database.HDBC Data.Ratio Control.Monad> (fromSql . head . head) `liftM` (quickQuery db "select 1.231 ::numeric(10,8);" []) :: IO Rational -- still gives 1231 % 1000 but should be 1.21310000 in decimal notation -- or 1231000 % 1000000 in rational notation
The % notation is a rational, so 'infinite' precision. So '1 % 1' and '1000 % 1000' are exactly the same, semantically. It's like fractions instead of decimal digits. Why exactly do you need the precision information? Erik