SQL> select 'xxxx'oooo' from dual;
ERROR:
ORA-01756: quoted string not properly terminated
SQL> select "xxxx'oooo" from dual;
select "xxxx'oooo" from dual
*
ERROR at line 1:
ORA-00904: "xxxx'oooo": invalid identifier
SQL> select q'[xxxx'oooo]' from dual;
Q'[XXXX'O
---------
xxxx'oooo