set constraints all deferred;这个语句为什么不能写在过程中？

Question

14:21:11 SQL> create or replace procedure tes
14:21:25   2  as
14:21:25   3  begin
14:21:25   4    execute immediate 'set constraint all deferred';
14:21:25   5  end;
14:21:25   6  /过程已创建。已用时间:  00: 00: 00.15
you can also execute
14:21:26 SQL> create or replace procedure tes
14:21:29   2  as
14:21:29   3  begin
14:21:29   4    execute immediate 'alter session set constraints= deferred';
14:21:29   5  end;
14:21:29   6  /过程已创建。已用时间:  00: 00: 00.15

Answer 1

为什么要用 execute 
oracle真是弱智呀.