Consider the following:
select f, count from (select CCHAR9, round(regr_syy(CDECIMAL9_2, length(CCHAR9)), 8) f from datatypetestm1 group by 1) a group by f order by f desc;

in this case, f is 0.00000 on one row and -0.00000 on another. One would expect the -0.000000 to sort last, but that is not the case, at least sometimes.