Is the round() function implemented differently for double precision than for numeric? Forgive me if this exists somewhere in the documentation, but I can't seem to find it. I've noticed with 9.6 on OSX, the .5 rounding is handled differently between the types. (I haven't tested other versions, yet.) For double precision values, even whole numbers are rounded down, yet for odds they are rounded up. For numeric values, all .5 numbers are rounded up. psql (9.6.3) Type "help" for help. postgres=# \x Expanded display is on. postgres=# select round(cast(1230.5 as double precision)) as round_double_even_0 postgres-# ,round(cast(1231.5 as double precision)) as round_double_odd_1 postgres-# ,round(cast(1232.5 as double precision)) as round_double_even_2 postgres-# ,round(cast(1233.5 as double precision)) as round_double_odd_3 postgres-# ,round(cast(1234.5 as double precision)) as round_double_even_4 postgres-# ,round(cast(1235.5 as double precision)) as round_double_odd_5 postgres-# ; -[ RECORD 1 ]-------+----- round_double_even_0 | 1230 round_double_odd_1 | 1232 round_double_even_2 | 1232 round_double_odd_3 | 1234 round_double_even_4 | 1234 round_double_odd_5 | 1236 postgres=# select round(cast(1230.5 as numeric)) as round_numeric_even_0 postgres-# ,round(cast(1231.5 as numeric)) as round_numeric_odd_1 postgres-# ,round(cast(1232.5 as numeric)) as round_numeric_even_2 postgres-# ,round(cast(1233.5 as numeric)) as round_numeric_odd_3 postgres-# ,round(cast(1234.5 as numeric)) as round_numeric_even_4 postgres-# ,round(cast(1235.5 as numeric)) as round_numeric_odd_5 postgres-# ; -[ RECORD 1 ]--------+----- round_numeric_even_0 | 1231 round_numeric_odd_1 | 1232 round_numeric_even_2 | 1233 round_numeric_odd_3 | 1234 round_numeric_even_4 | 1235 round_numeric_odd_5 | 1236 postgres=# select round(1230.5) as round_even_0 ,round(1231.5) as round_odd_1 ,round(1232.5) as round_even_2 ,round(1233.5) as round_odd_3 ,round(1234.5) as round_even_4 ,round(1235.5) as round_odd_5 ; -[ RECORD 1 ]+----- round_even_0 | 1231 round_odd_1 | 1232 round_even_2 | 1233 round_odd_3 | 1234 round_even_4 | 1235 round_odd_5 | 1236 postgres=# \q Why does the algorithm vary by data type? Or is something entirely different happening? |
