oracle优化--表优化（临时表）
一、创建临时表与普通表
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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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