PL/SQL：將數據類型分配給變量

Question

有沒有辦法做到這一點？我想要這樣做：

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; 

謝謝！

Answer 1

你可以這樣說：

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

但是，爲什麼？