How can I print out all possible letter combinations a given phone number can represent?

Question

I just tried for my first programming interview and one of the questions was to write a program that given a 7 digit telephone number, could print all possible combinations

Answer 1

Oracle SQL: Usable with any phone number length and can easily support localization.

CREATE TABLE digit_character_map (digit number(1), character varchar2(1));

SELECT replace(permutations,' ','') AS permutations
FROM (SELECT sys_connect_by_path(map.CHARACTER,' ') AS permutations, LEVEL AS lvl
      FROM digit_character_map map 
      START WITH map.digit = substr('12345',1,1)
      CONNECT BY   digit = substr('12345',LEVEL,1))
WHERE lvl = length('12345');