删除某个用户下的所有表
1、

select   'Drop   table   '||table_name||';'    
        from   all_tables  
        where   owner='要删除的用户名（注意要大写）';  

2、

删除所有表


以用户test为例

for example:

declare
cursor cur1 is select table_name from dba_tables where owner='TEST';
begin
  for cur2 in cur1 loop
    execute immediate 'drop table test.'||cur2.table_name;
  end loop;
end;

3、这个删除当前用户的所有对象(表、视图、触发器、存储过程、函数)

    没试过

DECLARE
TYPE name_list IS TABLE OF VARCHAR2(40);
TYPE type_list IS TABLE OF VARCHAR2(20);

Tab_name name_list:=name_list();
Tab_type type_list:=type_list();

sql_str VARCHAR2(500);
BEGIN
sql_str := 'select uo.object_name,uo.object_type from user_objects uo where uo.object_type not in(''INDEX'',''LOB'') order by uo.object_type desc';
EXECUTE IMMEDIATE sql_str BULK COLLECT INTO tab_name,tab_type;

FOR i IN Tab_name.FIRST.. Tab_name.LAST LOOP
sql_str := 'DROP ' || Tab_type(i) || ' ' || Tab_name(i);
EXECUTE IMMEDIATE sql_str;
END LOOP;
END;