PostgreSQL 除法保留小数点

bill=# select 1/2::float8;
 ?column?
----------
 0.5
(1 row)
bill=# select 1/2::numeric;
 ?column?
------------------------
 0.50000000000000000000
(1 row)
bill=# select 1::money/2;
 ?column?
----------
 $0.50
(1 row)