ORA-10921: Cannot drop tablespace belonging to default temporary tablespace group

Trying to drop a temporary tablespace which belongs to a default temporary tablespace group.

SQL> select * from DBA_TABLESPACE_GROUPS;

GROUP_NAME          TABLESPACE_NAME
------------------- ------------------------------
TEMP_OLTP           TEMP
TEMP_OLTP           TEMP2
TEMP_OLTP           TEMP3

SQL> DROP TABLESPACE temp2 INCLUDING CONTENTS AND DATAFILES;
DROP TABLESPACE temp2 INCLUDING CONTENTS AND DATAFILES
*
ERROR at line 1:
ORA-10921: Cannot drop tablespace belonging to default temporary tablespace group


SQL> DROP TABLESPACE temp3 INCLUDING CONTENTS AND DATAFILES;
 DROP TABLESPACE temp3 INCLUDING CONTENTS AND DATAFILES
*
ERROR at line 1:
ORA-10921: Cannot drop tablespace belonging to default temporary tablespace group

Change default temporary tablespace from  temporary tablespace group TEMP_OLTP to a temporary tablespace TEMP.:

SQL> alter pluggable database default temporary tablespace temp;

Pluggable database altered.

Now drop temporary tablespaces:

SQL> DROP TABLESPACE temp2 INCLUDING CONTENTS AND DATAFILES;

Tablespace dropped.

SQL> DROP TABLESPACE temp3 INCLUDING CONTENTS AND DATAFILES;

Tablespace dropped.

SQL> select * from DBA_TABLESPACE_GROUPS;

GROUP_NAME      TABLESPACE_NAME
--------------- -----------------
TEMP_OLTP        TEMPA

Make temporary tablespace group as default again:

SQL> alter pluggable database default temporary tablespace TEMP_OLTP;

Pluggable database altered.