extra_float_digits (integer) ​

This parameter adjusts the number of digits displayed for floating-point values. The parameter value is added to the standard number of digits. The value can be set as high as 3, to include partially-significant digits; this is especially useful for dumping float data that needs to be restored exactly. Or it can be set negative to suppress unwanted digits.

For example, note the difference in query results against a REAL column when extra_float_digits is set to 3 versus 0:

reset extra_float_digits;

create table extra_float as select avg_att::real from team where avg_att>0;
SELECT 20
select * from extra_float;
 avg_att 
---------
  35.776
  20.594
  24.631
  34.91
  59.944
  33.69
  11.189
  ...
(20 rows)

set extra_float_digits to 3;
SET
create table extra_float_3 as select avg_att::real from team where avg_att>0;
SELECT 20
select * from extra_float_3;
  avg_att   
------------
 35.776001
 20.5939999
 24.6310005
 34.9099998
 59.9440002
 33.6899986
 11.1890001
 ...
(20 rows)

See also real data types.