Here is how you could create such a table:
SELECT LEVEL AS id, REGEXP_SUBSTR('A,B,C,D', '[^,]+', 1, LEVEL) AS data
FROM dual
CONNECT BY REGEXP_SUBSTR('A,B,C,D', '[^,]+', 1, LEVEL) IS NOT NULL;
With a little bit of tweaking (i.e., replacing the ,
in [^,]
with a variable) you could write such a function to return a table.