oracel 基础知识

create or replace procedure proc_stu(sid number,age in out number)
is
begin
  update student set stuAge=stuAge+age where stuId=sid;
  select avg(stuAge) into age from student;
end proc_stu;
---
declare
    id number:=&id;
    age1 number:=&age1;--5
begin
  proc_stu(id,age1);
  dbms_output.put_line('平均年龄：'||age1);
end;
里面的in out不是很明白？