test=# select '1000000'::real + '5'::real;
?column?
----------
1e+06
(1 row)
test=# select '1000000'::real + '6'::real;
?column?
-------------
1.00001e+06
(1 row)
test=# select '0.1'::real + 0.0;
?column?
-------------------
0.100000001490116
(1 row)