方法1：

    drop user XXXX cascade

    drop tablespace XXXX INCLUDING CONTENTS;

方法2：

set heading off;
set feedback off;
spool c:\dropobj.sql;
  prompt --Drop constraint
 select 'alter table '||table_name||' drop constraint '||constraint_name||' ;' from user_constraints where constraint_type='R';
 prompt --Drop tables
 select 'drop table '||table_name ||';' from user_tables;
 
 prompt --Drop view
 select 'drop view ' ||view_name||';' from user_views;
 
 prompt --Drop sequence
 select 'drop sequence ' ||sequence_name||';' from user_sequences;
 
 prompt --Drop function
 select 'drop function ' ||object_name||';'  from user_objects  where object_type='FUNCTION';

 prompt --Drop procedure
 select 'drop procedure '||object_name||';' from user_objects  where object_type='PROCEDURE';
 
 prompt --Drop package
 prompt --Drop package body
 select 'drop package '|| object_name||';' from user_objects  where object_type='PACKAGE';

 prompt --Drop database link
 select 'drop database link '|| object_name||';' from user_objects  where object_type='DATABASE LINK';
 
spool off;
set heading on;
set feedback on;

@@c:\dropobj.sql;
host del c:\dropobj.sql;



注释：
1.上面这个语句，在pl/sql里面是放在命令里面执行的。
2.set heading off; 意思就是关闭表头。如果不关闭，写入dropobj.sql文件中就会带有结果集的表头如：
'DROPTABLE'||TABLE_NAME||';'
------------------------------------------
drop table TEACHER;
实际上我们需要的是“drop table TEACHER;”，“'DROPTABLE'||TABLE_NAME||';'
”就是表头。
3.set feedback off; 意思就是关闭回显。如果不关闭，写入dropobj.sql文件中就会带有返回结果集的大小等信息，如："137 rows selected"
4.spool c:\dropobj.sql; 把结果集写入这个文件。spool off; 结束写入。
5.@@c:\dropobj.sql; 执行这个sql
6.host del c:\dropobj.sql; 删除主机上这文件。
7.CONSTRAINT_TYPE 就是键的类型：
Sql代码 复制代码

   1. C (check constraint on a table)    
   2. P (primary key)    
   3. U (unique key)   
   4. R (referential integrity)   
   5. V (with check option, on a view)   
   6. O (with read only, on a view)  

C (check constraint on a table)
P (primary key)
U (unique key)
R (referential integrity)
V (with check option, on a view)
O (with read only, on a view)