For one that satisfies only the second statement, if f(a+b)=f(a*b), then f(a+0)=f(a*0), so
f(a) is f(0) for any a, so the second statement alone assures us that this function is constant, but there is no way to know what constant with only the fact f(a+b)=f(a*b) .
Now combine your second...