Oracle学习笔记（九）

全局临时表自动处理数据：

drop table ljb_tmp_session;
create global temporary table ljb_tmp_session on commit preserve rows as select  * from dba_objects where 1=2;
select table_name,temporary,duration from user_tables  where table_name='LJB_TMP_SESSION';
drop table  ljb_tmp_transaction;
create global temporary table ljb_tmp_transaction on commit delete rows as select * from dba_objects where 1=2;
select table_name, temporary, DURATION from user_tables  where table_name='LJB_TMP_TRANSACTION';

insert all 
   into  ljb_tmp_transaction
   into  ljb_tmp_session
select * from dba_objects;

select session_cnt,transaction_cnt from (select count(*) session_cnt from ljb_tmp_session),
 (select count(*) transaction_cnt from ljb_tmp_transaction);

commit;
 
select session_cnt,transaction_cnt from (select count(*) session_cnt from ljb_tmp_session),
(select count(*) transaction_cnt from ljb_tmp_transaction);


select session_cnt,transaction_cnt from (select count(*) session_cnt from ljb_tmp_session),
(select count(*) transaction_cnt from ljb_tmp_transaction);

　　不同session数据独立：

drop table ljb_tmp_session;
create global temporary table ljb_tmp_session on commit preserve rows as select  * from dba_objects where 1=2;
select table_name,temporary,duration from user_tables  where table_name='LJB_TMP_SESSION';
drop table  ljb_tmp_transaction;
create global temporary table ljb_tmp_transaction on commit delete rows as select * from dba_objects where 1=2;
select table_name, temporary, DURATION from user_tables  where table_name='LJB_TMP_TRANSACTION';

--不同session的例子试验基于sesssion 的临时表即可了，不用试验另外一个了。
---连上session 1
 insert into ljb_tmp_session select * from dba_objects　where rownum<=10;
 --可以体会提交，基于session 的提交并清理数据
 commit;
 select count(*) from ljb_tmp_session;


  COUNT(*)
----------
    10 
 
---不退出session 1，继续登录session 2
insert into ljb_tmp_session select * from dba_objects　where rownum<=20;
commit;
select count(*) from ljb_tmp_session;

  COUNT(*)
----------
    20

　　产生日志较少：

全局临时表是否在同样delete ,insert 和update 的情况下，产生的redo比普通表要少的多。

sqlplus "/ as sysdba"
grant all on v_$mystat to ljb;
grant all on v_$statname to ljb;
connect  ljb/ljb
drop table t purge;
create table t as select * from dba_objects ;
--以下创建视图，方便后续直接用select * from v_redo_size进行查询
create or replace view v_redo_size as
    select a.name,b.value
    from v$statname a,v$mystat b
    where a.statistic#=b.statistic#
    and a.name='redo size';
    
    
select * from v_redo_size;

--中间输入你的删除插入更新的动作

select * from v_redo_size;    

两次相减就是产生的redo量

　　索引组织表：

--必须有主键！
---分别建索引组织表和普通表进行试验
set autotrace off
drop table heap_addresses purge;
drop table iot_addresses purge;
create table heap_addresses
   (empno    number(10),
    addr_type varchar2(10),
    street    varchar2(10),
    city      varchar2(10),
    state     varchar2(2),
    zip       number,
    primary key (empno)
   )
/

create table iot_addresses
   (empno    number(10),
    addr_type varchar2(10),
    street    varchar2(10),
    city      varchar2(10),
    state     varchar2(2),
    zip       number,
   primary key (empno)
   )
   organization index
/
insert into heap_addresses
   select object_id,'WORK','123street','washington','DC',20123
   from all_objects;
insert into iot_addresses
    select object_id,'WORK','123street','washington','DC',20123
    from all_objects;
commit;

---分别比较索引组织表和普通表的查询性能
set linesize 1000
set autotrace traceonly
select * from heap_addresses where empno=22;
SQL> select * from heap_addresses where empno=22;

执行计划
----------------------------------------------------------------------------------------------
| Id  | Operation                   | Name           | Rows  | Bytes | Cost (%CPU)| Time     |
----------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT            |                |     1 |    50 |     1   (0)| 00:00:01 |
|   1 |  TABLE ACCESS BY INDEX ROWID| HEAP_ADDRESSES |     1 |    50 |     1   (0)| 00:00:01 |
|*  2 |   INDEX UNIQUE SCAN         | SYS_C0013751   |     1 |       |     1   (0)| 00:00:01 |
----------------------------------------------------------------------------------------------
统计信息
----------------------------------------------------------
          0  recursive calls
          0  db block gets
          3  consistent gets
          0  physical reads
          0  redo size
        659  bytes sent via SQL*Net to client
        405  bytes received via SQL*Net from client
          1  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          1  rows processed
          
          
select * from iot_addresses where empno=22;

执行计划
----------------------------------------------------------------------------------------
| Id  | Operation         | Name               | Rows  | Bytes | Cost (%CPU)| Time     |
----------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT  |                    |     1 |    50 |     1   (0)| 00:00:01 |
|*  1 |  INDEX UNIQUE SCAN| SYS_IOT_TOP_104441 |     1 |    50 |     1   (0)| 00:00:01 |
----------------------------------------------------------------------------------------
统计信息
----------------------------------------------------------
          0  recursive calls
          0  db block gets
          2  consistent gets
          0  physical reads
          0  redo size
        751  bytes sent via SQL*Net to client
        416  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          1  rows processed
 

　　簇表：

--构造环境
--注意这个删除的先后顺序，否则会报ORA-00951: 簇非空
set autotrace off
drop table cust_orders;
drop cluster shc;

CREATE CLUSTER shc
(
   cust_id     NUMBER,
   order_dt    timestamp SORT
)
HASHKEYS 10000
HASH IS cust_id
SIZE  8192
/
CREATE TABLE cust_orders
(  cust_id       number,
   order_dt      timestamp SORT,
   order_number  number,
   username      varchar2(30),
   ship_addr     number,
   bill_addr     number,
   invoice_num   number
)
CLUSTER shc ( cust_id, order_dt )
/


---开始执行分析
set autotrace traceonly 
variable x number
--以下是利用有序散列聚族表的方法，发现排序被避免
select cust_id, order_dt, order_number
  from cust_orders
 where cust_id = :x
 order by order_dt;
 

执行计划
----------------------------------------------------------------------
| Id  | Operation         | Name        | Rows  | Bytes | Cost (%CPU)|
----------------------------------------------------------------------
|   0 | SELECT STATEMENT  |             |     1 |    39 |     0   (0)|
|*  1 |  TABLE ACCESS HASH| CUST_ORDERS |     1 |    39 |            |
----------------------------------------------------------------------
统计信息
----------------------------------------------------------
          0  recursive calls
          0  db block gets
          0  consistent gets
          0  physical reads
          0  redo size
        416  bytes sent via SQL*Net to client
        404  bytes received via SQL*Net from client
          1  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          0  rows processed
 
--以下是普通方法，排序不可避免
select job, hiredate, empno
  from scott.emp
 where job = 'CLERK'
 order by hiredate;

执行计划
---------------------------------------------------------------------------
| Id  | Operation          | Name | Rows  | Bytes | Cost (%CPU)| Time     |
---------------------------------------------------------------------------
|   0 | SELECT STATEMENT   |      |     3 |    60 |     4  (25)| 00:00:01 |
|   1 |  SORT ORDER BY     |      |     3 |    60 |     4  (25)| 00:00:01 |
|*  2 |   TABLE ACCESS FULL| EMP  |     3 |    60 |     3   (0)| 00:00:01 |
---------------------------------------------------------------------------
统计信息
----------------------------------------------------------
          0  recursive calls
          0  db block gets
          7  consistent gets
          0  physical reads
          0  redo size
        640  bytes sent via SQL*Net to client
        415  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          1  sorts (memory)
          0  sorts (disk)
          4  rows processed

　　外键索引性能：

drop table t_p cascade constraints purge;
drop table t_c cascade constraints purge;

CREATE TABLE T_P (ID NUMBER, NAME VARCHAR2(30));
ALTER TABLE T_P ADD CONSTRAINT  T_P_ID_PK  PRIMARY KEY (ID);
CREATE TABLE T_C (ID NUMBER, FID NUMBER, NAME VARCHAR2(30));

ALTER TABLE T_C ADD CONSTRAINT FK_T_C FOREIGN KEY (FID) REFERENCES T_P (ID);

INSERT INTO T_P SELECT ROWNUM, TABLE_NAME FROM ALL_TABLES;
INSERT INTO T_C SELECT ROWNUM, MOD(ROWNUM, 1000) + 1, OBJECT_NAME  FROM ALL_OBJECTS;
COMMIT;

---外键未建索引前的表连接性能分析
set autotrace traceonly
set linesize 1000
SELECT A.ID, A.NAME, B.NAME FROM T_P A, T_C B WHERE A.ID = B.FID AND A.ID = 880;

执行计划
------------------------------------------------------------------------------------------
| Id  | Operation                    | Name      | Rows  | Bytes | Cost (%CPU)| Time     |
------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT             |           |    71 |  4260 |   137   (1)| 00:00:02 |
|   1 |  NESTED LOOPS                |           |    71 |  4260 |   137   (1)| 00:00:02 |
|   2 |   TABLE ACCESS BY INDEX ROWID| T_P       |     1 |    30 |     0   (0)| 00:00:01 |
|*  3 |    INDEX UNIQUE SCAN         | T_P_ID_PK |     1 |       |     0   (0)| 00:00:01 |
|*  4 |   TABLE ACCESS FULL          | T_C       |    71 |  2130 |   137   (1)| 00:00:02 |
------------------------------------------------------------------------------------------
统计信息
----------------------------------------------------------
          0  recursive calls
          0  db block gets
        452  consistent gets
          0  physical reads
          0  redo size
       3605  bytes sent via SQL*Net to client
        459  bytes received via SQL*Net from client
          6  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
         72  rows processed
         
         
--外键建索引后的表连接性能分析
CREATE INDEX IND_T_C_FID ON T_C (FID);
SELECT A.ID, A.NAME, B.NAME FROM T_P A, T_C B WHERE A.ID = B.FID AND A.ID = 880;
执行计划
--------------------------------------------------------------------------------------------
| Id  | Operation                    | Name        | Rows  | Bytes | Cost (%CPU)| Time     |
--------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT             |             |    72 |  4320 |    69   (0)| 00:00:01 |
|   1 |  NESTED LOOPS                |             |    72 |  4320 |    69   (0)| 00:00:01 |
|   2 |   TABLE ACCESS BY INDEX ROWID| T_P         |     1 |    30 |     0   (0)| 00:00:01 |
|*  3 |    INDEX UNIQUE SCAN         | T_P_ID_PK   |     1 |       |     0   (0)| 00:00:01 |
|   4 |   TABLE ACCESS BY INDEX ROWID| T_C         |    72 |  2160 |    69   (0)| 00:00:01 |
|*  5 |    INDEX RANGE SCAN          | IND_T_C_FID |    72 |       |     1   (0)| 00:00:01 |
--------------------------------------------------------------------------------------------
统计信息
----------------------------------------------------------
          0  recursive calls
          0  db block gets
         83  consistent gets
          0  physical reads
          0  redo size
       3605  bytes sent via SQL*Net to client
        459  bytes received via SQL*Net from client
          6  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
         72  rows processed 

　　外键与锁：

--外键索引性能研究之准备
drop table t_p cascade constraints purge;
drop table t_c cascade constraints purge;

CREATE TABLE T_P (ID NUMBER, NAME VARCHAR2(30));
ALTER TABLE T_P ADD CONSTRAINT  T_P_ID_PK  PRIMARY KEY (ID);
CREATE TABLE T_C (ID NUMBER, FID NUMBER, NAME VARCHAR2(30));

ALTER TABLE T_C ADD CONSTRAINT FK_T_C FOREIGN KEY (FID) REFERENCES T_P (ID);

INSERT INTO T_P SELECT ROWNUM, TABLE_NAME FROM ALL_TABLES;
INSERT INTO T_C SELECT ROWNUM, MOD(ROWNUM, 1000) + 1, OBJECT_NAME  FROM ALL_OBJECTS;
COMMIT;

create index idx_IND_T_C_FID on T_C(FID);

外键有索引，没有死锁情况产生
--首先开启会话1
select sid from v$mystat where rownum=1;
DELETE T_C WHERE FID = 2;

--接下来开启会话2，也就是开启一个新的连接
select sid from v$mystat where rownum=1;
DELETE T_P WHERE ID = 2000;

外键索引先删除
drop index  idx_IND_T_C_FID;


外键索引删除后，立即有锁相关问题
--首先开启会话1
select sid from v$mystat where rownum=1;
DELETE T_C WHERE ID = 2;
--接下来开启会话2，也就是开启一个新的连接
select sid from v$mystat where rownum=1;
 
--然后执行如下进行观察
DELETE T_P WHERE ID = 2000;
--居然发现卡住半天不动了！

　　普通索引改主键：

drop table t_p cascade constraints purge;
CREATE TABLE t_p
(order_id NUMBER(3),
 item_id NUMBER(2),
 comments varchar2(400));
CREATE INDEX ord_itm_idx ON t_p(order_id,item_id);

alter table t_p add constraint ord_itm_id_pk primary key (order_id,item_id) using index ord_itm_idx ;

---不需要如此操作(差别只是索引名不一样而已）
drop index ord_itm_idx;
alter table t_p add constraint ord_itm_id_pk primary key (order_id,item_id);　

主键DISABLE再ENABLE后，外键需要重新生效

drop table t_p  cascade constraints purge; 
create table t_p (dept_id number,emp_name varchar2(20),emp_id number);
alter  table t_p add constraints pk_dept_id PRIMARY KEY  (dept_id);
ALTER  TABLE t_p ADD CONSTRAINT FK_T_F FOREIGN KEY (emp_id) REFERENCES T_P (dept_id) ;
select CONSTRAINT_TYPE,TABLE_NAME,STATUS from user_constraints t where t.constraint_name in ('PK_DEPT_ID','FK_T_F');
ALTER TABLE t_p DISABLE CONSTRAINT pk_dept_id CASCADE;
select CONSTRAINT_TYPE,TABLE_NAME,STATUS from user_constraints t where t.constraint_name in ('PK_DEPT_ID','FK_T_F');
ALTER TABLE t_p ENABLE CONSTRAINT pk_dept_id ;
select CONSTRAINT_TYPE,TABLE_NAME,STATUS from user_constraints t where t.constraint_name in ('PK_DEPT_ID','FK_T_F');
alter table t_p enable constraint FK_T_F;
select CONSTRAINT_TYPE,TABLE_NAME,STATUS from user_constraints t where t.constraint_name in ('PK_DEPT_ID','FK_T_F');

　　主键约束有延迟约束到提交才验证的功能

drop table test cascade constraints;
create table test as select rownum object_id,object_name from dba_objects where rownum<=20;
ALTER TABLE test ADD CONSTRAINT pk_object_id PRIMARY KEY(object_id) DEFERRABLE INITIALLY DEFERRED;
INSERT INTO test VALUES (21,'ABC'); 
INSERT INTO test VALUES (21,'EFG');
COMMIT;
SET CONSTRAINT pk_object_id IMMEDIATE;
INSERT INTO test VALUES (1,'LATA');
INSERT INTO test VALUES (2,'KING');
COMMIT;

　　主外键设计其他约束条件：

drop table test cascade constraints;
create table test as select rownum object_id,object_name from dba_objects where rownum<=20;
ALTER TABLE test ADD CONSTRAINT pk_object_id PRIMARY KEY(object_id) DEFERRABLE INITIALLY DEFERRED;
INSERT INTO test VALUES (21,'ABC'); 
INSERT INTO test VALUES (21,'EFG');
COMMIT;
SET CONSTRAINT pk_object_id IMMEDIATE;
INSERT INTO test VALUES (1,'LATA');
INSERT INTO test VALUES (2,'KING');
COMMIT;

　　表压缩：

---压缩表可减少数据量，从而减少IO

DROP TABLE t purge;

CREATE TABLE t NOCOMPRESS AS
SELECT rownum AS n, rpad(' ',500,mod(rownum,15)) AS pad
FROM dual
CONNECT BY level <= 200000;

execute dbms_stats.gather_table_stats(ownname=>user, tabname=>'t');

--未压缩的表当前情况
SELECT table_name, blocks,compression  FROM user_tables WHERE table_name = 'T';
TABLE_NAME                         BLOCKS COMPRESS
------------------------------ ---------- --------
T                                   14449 DISABLED
set autotrace traceonly
select count(*) from t;

执行计划
-------------------------------------------------------------------
| Id  | Operation          | Name | Rows  | Cost (%CPU)| Time     |
-------------------------------------------------------------------
|   0 | SELECT STATEMENT   |      |     1 |  3922   (1)| 00:00:48 |
|   1 |  SORT AGGREGATE    |      |     1 |            |          |
|   2 |   TABLE ACCESS FULL| T    |   200K|  3922   (1)| 00:00:48 |
-------------------------------------------------------------------
统计信息
----------------------------------------------------------
          0  recursive calls
          0  db block gets
      14297  consistent gets
          0  physical reads
          0  redo size
        423  bytes sent via SQL*Net to client
        416  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          1  rows processed
      
--开始压缩表
set autotrace off
ALTER TABLE t MOVE COMPRESS;
execute dbms_stats.gather_table_stats(ownname=>user, tabname=>'t');
SELECT table_name, blocks,compression  FROM user_tables WHERE table_name = 'T';
TABLE_NAME                         BLOCKS COMPRESS
------------------------------ ---------- --------
T                                    2639 ENABLED

set autotrace traceonly 
select count(*) from t;

执行计划
-------------------------------------------------------------------
| Id  | Operation          | Name | Rows  | Cost (%CPU)| Time     |
-------------------------------------------------------------------
|   0 | SELECT STATEMENT   |      |     1 |   718   (1)| 00:00:09 |
|   1 |  SORT AGGREGATE    |      |     1 |            |          |
|   2 |   TABLE ACCESS FULL| T    |   200K|   718   (1)| 00:00:09 |
-------------------------------------------------------------------
统计信息
----------------------------------------------------------
          0  recursive calls
          0  db block gets
       2595  consistent gets
          0  physical reads
          0  redo size
        423  bytes sent via SQL*Net to client
        416  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          1  rows processed
          
注意：压缩后的表更新的开销会更大，查询耗费的CPU也更多。所以压缩表一般适合在更新比较少，且CPU消耗不大，IO消耗很大系统中试用。

　　索引压缩：

---压缩索引(联合索引的压缩层度会高一些）
DROP TABLE t1 purge;

CREATE TABLE t1 AS select * from dba_objects;
alter table T1 modify owner not null;
alter table T1 modify object_name not null;
alter table T1 modify object_type not null;
insert  into t1 select * from t1;
insert  into t1 select * from t1;
commit;
create index idx1_object_union  on t1(owner,object_type,object_name);
execute dbms_stats.gather_index_stats(ownname=>user, indname=>'idx1_object_union');

--未压缩索引的当前情况
SELECT t.index_name,t.compression,t.leaf_blocks,t.blevel  FROM user_indexes t WHERE index_name = 'IDX1_OBJECT_UNION';

INDEX_NAME                     COMPRESS LEAF_BLOCKS     BLEVEL
------------------------------ -------- ----------- ----------
IDX1_OBJECT_UNION              DISABLED        2043          2

--开始压缩索引
drop table t2 purge;
create table t2 as select * from t1;
alter table T2 modify owner not null;
alter table T2 modify object_name not null;
alter table T2 modify object_type not null;
create index idx2_object_union  on t2(owner,object_type,object_name);
ALTER index  idx2_object_union  rebuild  COMPRESS;
execute dbms_stats.gather_index_stats(ownname=>user, indname=>'idx2_object_union');

SELECT t.index_name,t.compression,t.leaf_blocks,t.blevel  FROM user_indexes t WHERE index_name = 'IDX2_OBJECT_UNION';

INDEX_NAME                     COMPRESS LEAF_BLOCKS     BLEVEL
------------------------------ -------- ----------- ----------
IDX2_OBJECT_UNION              ENABLED          907          2


set linesize 1000
set autotrace traceonly
select count(*) from t1 ;

执行计划
-----------------------------------------------------------------------------------
| Id  | Operation             | Name              | Rows  | Cost (%CPU)| Time     |
-----------------------------------------------------------------------------------
|   0 | SELECT STATEMENT      |                   |     1 |   572   (1)| 00:00:07 |
|   1 |  SORT AGGREGATE       |                   |     1 |            |          |
|   2 |   INDEX FAST FULL SCAN| IDX1_OBJECT_UNION |   251K|   572   (1)| 00:00:07 |
-----------------------------------------------------------------------------------
统计信息
----------------------------------------------------------
          0  recursive calls
          0  db block gets
       2067  consistent gets
          0  physical reads
          0  redo size
        425  bytes sent via SQL*Net to client
        415  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          1  rows processed
          
select count(*) from t2 ;

执行计划
-----------------------------------------------------------------------------------
| Id  | Operation             | Name              | Rows  | Cost (%CPU)| Time     |
-----------------------------------------------------------------------------------
|   0 | SELECT STATEMENT      |                   |     1 |   258   (1)| 00:00:04 |
|   1 |  SORT AGGREGATE       |                   |     1 |            |          |
|   2 |   INDEX FAST FULL SCAN| IDX2_OBJECT_UNION |   282K|   258   (1)| 00:00:04 |
-----------------------------------------------------------------------------------
统计信息
----------------------------------------------------------
          0  recursive calls
          0  db block gets
        922  consistent gets
          0  physical reads
          0  redo size
        425  bytes sent via SQL*Net to client
        415  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          1  rows processed

　　列值如何存放：

--什么类型就放什么值，否则会发生类型转换，导致系能问题！
--（是存放字符的字段就设varchar2类型,是存放数值的字段就设置number类型,是存放日期的字段就设置date类型）

--举例说明：
drop table t_col_type purge;
create table t_col_type(id varchar2(20),col2 varchar2(20),col3 varchar2(20));
insert into t_col_type select rownum,'abc','efg' from dual connect by level<=10000;
commit;
create index idx_id on t_col_type(id);
set linesize 1000
set autotrace traceonly

select * from t_col_type where id=6;

执行计划
--------------------------------------------------------------------------------
| Id  | Operation         | Name       | Rows  | Bytes | Cost (%CPU)| Time     |
--------------------------------------------------------------------------------
|   0 | SELECT STATEMENT  |            |     1 |    36 |     9   (0)| 00:00:01 |
|*  1 |  TABLE ACCESS FULL| T_COL_TYPE |     1 |    36 |     9   (0)| 00:00:01 |
--------------------------------------------------------------------------------
   1 - filter(TO_NUMBER("ID")=6)
统计信息
----------------------------------------------------------
          0  recursive calls
          0  db block gets
         32  consistent gets
          0  physical reads
          0  redo size
        540  bytes sent via SQL*Net to client
        415  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          1  rows processed

--实际上只有如下写法才可以用到索引，这个很不应该，是什么类型的取值就设置什么样的字段。
          
select * from t_col_type where id='6';
执行计划
------------------------------------------------------------------------------------------
| Id  | Operation                   | Name       | Rows  | Bytes | Cost (%CPU)| Time     |
------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT            |            |     1 |    36 |     2   (0)| 00:00:01 |
|   1 |  TABLE ACCESS BY INDEX ROWID| T_COL_TYPE |     1 |    36 |     2   (0)| 00:00:01 |
|*  2 |   INDEX RANGE SCAN          | IDX_ID     |     1 |       |     1   (0)| 00:00:01 |
------------------------------------------------------------------------------------------
   2 - access("ID"='6')
统计信息
----------------------------------------------------------
          0  recursive calls
          0  db block gets
          4  consistent gets
          0  physical reads
          0  redo size
        544  bytes sent via SQL*Net to client
        415  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          1  rows processed   

　　过时的字段：

CHAR和LONG基本要被VARCHAR2和CLOB等替换，属于已经过时的字段类型。

其中CHAR不利扩展，且有可能浪费空间。
而LONG的更新查询操作极为麻烦！