SQL Generate Random Number

I have this table X with only one column, A. How can I generate a random number in each row, within specific values? Let's say I want random numbers to be either 1, 2 or 999 (3 numbers), I would have a column B looking something like this:

A | B
-----
12| 1
33| 999
67| 1
20| 2
... 

I've tried the dbms_random package but only to generate between 2 numbers, like this:

select X.*, round(dbms_random.value(1,2)) from X;

Any suggestions?