Possible To Parse A Column In A Select Statement?

I have a column called SEGMENTED_BLOCK sample data:
X,X,X
XX,XX,XX,
TYZC123456,X,X,
TOYZ654321,1234,777777

I need to do something that has the effect of

SELECT
(stuff before first comma) as FIRST_ITEM,
(stuff after first comma, but before second) as NEXT_ITEM,
(stuff after second comma but before third(if any)) as THIRD_ITEM
FROM SEGMENT_XREF
WHERE LOOKUP_ITEM = 12345
ORDER BY FIRST_ITEM

FIRST_ITEM is pretty easy, but it gets uglier fast.
My attempts are horrendously ugly nested checkindex and substring statements.
Is there an easier way?