PL SQL: read comma-separated input string

 select regexp_substr('SMITH,ALLEN,WARD,JONES','[^,]+', 1, level) from dual
   connect by regexp_substr('SMITH,ALLEN,WARD,JONES', '[^,]+', 1, level) is not null;


reference:
https://blogs.oracle.com/aramamoo/entry/how_to_split_comma_separated_string_and_pass_to_in_clause_of_select_statement