nanvl [Oracle SQL]

create table nanvl_test (a binary_float);

insert into nanvl_test values ( 42.42);
insert into nanvl_test values (-18.90);
insert into nanvl_test values ( 'NaN');

select nanvl(a, '999') from nanvl_test;

NANVL(A,'999')
--------------
    4.242E+001
    -1.89E+001
     9.99E+002