SQL & PL/SQL

I try to convert LONG data type to any character string data type (best char or varchar2) ?

e.g.

SELECT TO_LOB(DATA_DEFAULT) AS TST1 FROM USER_TAB_COLS
WHERE DATA_DEFAULT IS NOT NULL ;

Any idea?

ORA-00932: inconsistent datatypes: expected - got LONG
00932. 00000 - "inconsistent datatypes: expected %s got %s"
*Cause:
*Action:
Error at Line: 4 Column: 8