Oracle中的5个问题 - Oracle / 基础和管理

如题:
1.16进制数在转化成10进制数时出错
SQL code:

SQL> select to_char(125,'xxxx') from dual;

TO_CHAR(125,'XXXX')
--------------------------------------------------------------------------------
7d

SQL> select to_char(7d,'xxx') from dual;

TO_CHAR(7.0E+000D,'XXX')
--------------------------------------------------------------------------------
7

SQL> select to_char(to_char(125,'xxxx'),'xxx') from dual;

select to_char(to_char(125,'xxxx'),'xxx') from dual

ORA-01722: 无效数字


2.索引高度是什么一个概念: pga_aggregate_target?
3.analyze index indexname validate structure有什么用？--判断是否需要重建索引?
4.以下代码怎样才能输出“Test successed!”
SQL code:

SQL> set serveroutput on;
SQL> create or replace and compile java source named test_java as
2 public class FirstJava{
3 public static void test(){
4 System.out.println("Test successed!");
5 }
6 };
7 /

Java created

SQL>
SQL> create or replace procedure test_java is
2 language java name 'FirstJava.test()';
3 /

Procedure created

SQL> exec hello;

PL/SQL procedure successfully completed



5.外联接提高表连接的查询速度？

&nb