Andreas Pflug <pgadmin(at)pse-consulting(dot)de> writes:
> Well, to me it's not well-known that floating-point addition is not
> associative, do I need to re-learn my math?
regression=# select (1.0::float8 + (-1.0::float8)) + 1.0e-20::float8;
?column?
----------
1e-20
(1 row)
regression=# select 1.0::float8 + ((-1.0::float8) + 1.0e-20::float8);
?column?
----------
0
(1 row)
regards, tom lane