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oracle优化--表优化(临时表)

原创 Oracle 作者:wysyl1990 时间:2018-08-15 00:12:43 0 删除 编辑

一、创建临时表与普通表


SQL> CREATE GLOBAL TEMPORARY TABLE TMP_TEST ON COMMIT PRESERVE ROWS AS SELECT * FROM emp;


Table created.


SQL> select count(0) from TMP_TEST;


  COUNT(0)

----------

14


SQL> CREATE GLOBAL TEMPORARY TABLE TMP_TEST1 ON COMMIT DELETE ROWS AS SELECT * FROM emp;


Table created.


SQL> select count(0) from TMP_TEST1;


  COUNT(0)

----------

 14


SQL> create table tmp_test2 as select * from emp;


Table created.


SQL> select count(0) from TMP_TEST2;


  COUNT(0)

----------

14


--由于创建tmp_test2为ddl,所以TMP_TEST1数据被清空;


SQL> select count(0) from TMP_TEST1;


  COUNT(0)

----------

0


--关闭会话重新打开,TMP_TEST数据也被清空


SQL> select count(0) from TMP_TEST;


  COUNT(0)

----------

0


二、分别对副本表进行增删改操作,对比性能,可以发现以下差别:


新增时:临时表的cr=8,普通表cr=11

修改时:临时表的cr=3,cost=2;普通表cr=7,cost=3

删除时:临时表的cr=3,cost=2;普通表cr=7,cost=3


所以临时表如果作为运算中间表做增删改运算时性能皆比普通表高


SQL> insert into SCOTT.TMP_TEST SELECT * FROM SCOTT.emp;


14 rows created.


Rows (1st) Rows (avg) Rows (max)  Row Source Operation

---------- ---------- ----------  ---------------------------------------------------

         0          0          0  LOAD TABLE CONVENTIONAL  ( cr=8  pr=0 pw=0 time=548 us)

        14         14         14   TABLE ACCESS FULL EMP (cr=7 pr=0 pw=0 time=64 us cost=3 size=1218 card=14)


SQL> insert into SCOTT.TMP_TEST1 SELECT * FROM SCOTT.emp;


14 rows created.


Rows (1st) Rows (avg) Rows (max)  Row Source Operation

---------- ---------- ----------  ---------------------------------------------------

         0          0          0  LOAD TABLE CONVENTIONAL  ( cr=8 pr=0 pw=0 time=566 us)

        14         14         14   TABLE ACCESS FULL EMP (cr=7 pr=0 pw=0 time=63 us cost=3 size=1218 card=14)


SQL> insert into SCOTT.TMP_TEST2 SELECT * FROM SCOTT.emp;


14 rows created.


Rows (1st) Rows (avg) Rows (max)  Row Source Operation

---------- ---------- ----------  ---------------------------------------------------

         0          0          0  LOAD TABLE CONVENTIONAL  ( cr=11 pr=2 pw=0 time=784 us)

        14         14         14   TABLE ACCESS FULL EMP (cr=7 pr=0 pw=0 time=31 us cost=3 size=1218 card=14)


SQL> delete from SCOTT.TMP_TEST where SAL<=2500;


9 rows deleted.


Rows (1st) Rows (avg) Rows (max)  Row Source Operation

---------- ---------- ----------  ---------------------------------------------------

         0          0          0  DELETE  TMP_TEST ( cr=3 pr=0 pw=0 time=125 us)

         9          9          9   TABLE ACCESS FULL TMP_TEST (cr=3 pr=0 pw=0 time=50 us cost=2 size=117 card=9)


SQL> delete from SCOTT.TMP_TEST1 where SAL<=2500;


9 rows deleted.


Rows (1st) Rows (avg) Rows (max)  Row Source Operation

---------- ---------- ----------  ---------------------------------------------------

         0          0          0  DELETE  TMP_TEST1 ( cr=3 pr=0 pw=0 time=161 us)

         9          9          9   TABLE ACCESS FULL TMP_TEST1 (cr=3 pr=0 pw=0 time=77 us cost=2 size=117 card=9)


SQL> delete from SCOTT.TMP_TEST2 where SAL<=2500;


9 rows deleted.


Rows (1st) Rows (avg) Rows (max)  Row Source Operation

---------- ---------- ----------  ---------------------------------------------------

         0          0          0  DELETE  TMP_TEST2 ( cr=7 pr=0 pw=0 time=105 us)

         9          9          9   TABLE ACCESS FULL TMP_TEST2 (cr=7 pr=0 pw=0 time=13 us cost=3 size=117 card=9)


SQL> update SCOTT.TMP_TEST set sal=sal+100;


5 rows updated.


Rows (1st) Rows (avg) Rows (max)  Row Source Operation

---------- ---------- ----------  ---------------------------------------------------

         0          0          0  UPDATE  TMP_TEST ( cr=3 pr=0 pw=0 time=132 us)

         5          5          5   TABLE ACCESS FULL TMP_TEST (cr=3 pr=0 pw=0 time=46 us cost=2 size=65 card=5)


SQL> update SCOTT.TMP_TEST1 set sal=sal+100;


5 rows updated.


Rows (1st) Rows (avg) Rows (max)  Row Source Operation

---------- ---------- ----------  ---------------------------------------------------

         0          0          0  UPDATE  TMP_TEST1 ( cr=3 pr=0 pw=0 time=132 us)

         5          5          5   TABLE ACCESS FULL TMP_TEST1 (cr=3 pr=0 pw=0 time=34 us cost=2 size=65 card=5)


SQL> update SCOTT.TMP_TEST2 set sal=sal+100;


5 rows updated.


Rows (1st) Rows (avg) Rows (max)  Row Source Operation

---------- ---------- ----------  ---------------------------------------------------

         0          0          0  UPDATE  TMP_TEST2 ( cr=7 pr=0 pw=0 time=69 us)

         5          5          5   TABLE ACCESS FULL TMP_TEST2 (cr=7 pr=0 pw=0 time=15 us cost=3 size=65 card=5)


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