PL/SQL：将数据类型分配给变量

Question

有没有办法做到这一点？我想要这样做：

create or replace 
package SOME_PACKAGE as 
    filetype type is clob%type; --assign clob's filetype to a variable 
end SOME_PACKAGE; 
/

declare 
    clb SOME_PACKAGE.filetype; 
begin 
    dbms_lob.writeappend(clb, 1, 's'); 
end; 

谢谢！

Answer 1

你可以这样说：

create or replace 
package SOME_PACKAGE as 
    subtype filetype is clob; --assign clob's filetype to a variable 
end SOME_PACKAGE; 
/

但是，为什么？