SELECT string_col
FROM table1, table2
WHERE table1.numbera = table2.uniqueid
OR table1.number = table2.uniqueid;
Or a more complex method that fetches both strings at once:
SELECT t1.string, t2.string
FROM table1, table2 t1, table2 t2
WHERE table1.numbera = t1.id
AND table1.numberb = t2.id