oracle 11G 实验 in 和 exists 区别

遇到一个关于优化问题，大数据量的数据 in 和 exists 的区别

特地在自己机器上实验了一把

1.数据库版本

Oracle Database 11g Enterprise Edition Release 11.2.0.1.0

2.表

SCOTT.EMP

SCOTT.DEPT

--SCOTT.DEPT.DEPTNO是SCOTT.EMP.DEPTNO的外键

CREATE TABLE SCOTT.EMP1 AS SELECT * FROM SCOTT.EMP

CREATE TABLE SCOTT.DEPT1 AS SELECT * FROM SCOTT.DEPT

3.执行计划统计

select * from table(dbms_xplan.display_cursor('sql_id'))

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

1.RBO+主外键关系的执行计划

select /*+ rule */* from emp where emp.deptno in (select deptno from dept)    --6sk9v0wuwzbct

-=====================================================
SQL_ID  6sk9v0wuwzbct, child number 0
-------------------------------------
select /*+ rule */* from emp where emp.deptno in (select deptno from
dept)

Plan hash value: 3956160932

----------------------------------
| Id  | Operation         | Name |
----------------------------------
|   0 | SELECT STATEMENT  |      |
|*  1 |  TABLE ACCESS FULL| EMP  |
----------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

1 - filter("EMP"."DEPTNO" IS NOT NULL)

Note
-----
- rule based optimizer used (consider using cbo)

/*

基于规则的优化器如果存在主外键的时候会忽略掉dept表的扫描

*/

2.主外键 + RBO 的主外键exists操作

select /*+ rule */* from emp where exists (select 1 from dept where dept.deptno=emp.deptno)   --1b9t1auw0zpnc
--===============================================================
SQL_ID  1b9t1auw0zpnc, child number 0
-------------------------------------
select /*+ rule */* from emp where exists (select 1 from dept where
dept.deptno=emp.deptno)

Plan hash value: 1783302997

--------------------------------------
| Id  | Operation          | Name    |
--------------------------------------
|   0 | SELECT STATEMENT   |         |
|*  1 |  FILTER            |         |
|   2 |   TABLE ACCESS FULL| EMP     |
|*  3 |   INDEX UNIQUE SCAN| PK_DEPT |
--------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

1 - filter( IS NOT NULL)
3 - access("DEPT"."DEPTNO"=:B1)

Note
-----
- rule based optimizer used (consider using cbo)

/*

可以看到比in写法多了一次扫描

*/

3.无索引+RBO in操作的执行计划

select /*+ rule */* from emp1 where deptno in (select deptno from dept1)        --fwtdq5hj1w5v7
--===================================================
SQL_ID  fwtdq5hj1w5v7, child number 0
-------------------------------------
select /*+ rule */* from emp1 where deptno in (select deptno from dept1)

Plan hash value: 1261695393

------------------------------------------
| Id  | Operation             | Name     |
------------------------------------------
|   0 | SELECT STATEMENT      |          |
|   1 |  MERGE JOIN           |          |
|   2 |   SORT JOIN           |          |
|   3 |    TABLE ACCESS FULL  | EMP1     |
|*  4 |   SORT JOIN           |          |
|   5 |    VIEW               | VW_NSO_1 |
|   6 |     SORT UNIQUE       |          |
|   7 |      TABLE ACCESS FULL| DEPT1    |
------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

4 - access("DEPTNO"="DEPTNO")
filter("DEPTNO"="DEPTNO")

Note
-----
- rule based optimizer used (consider using cbo)

/*

就这个sql来看，是先把in中的子查询结果集计算完成并取唯一，然后在与EMP1表排序合并连接

会有大量的排序时间

*/

4.无索引+RBO exists操作执行计划

select /*+ rule */* from emp1 where exists (select 1 from dept1 where dept1.deptno=emp1.deptno)  --7cd23zjzhmyja
SQL_ID  7cd23zjzhmyja, child number 0
-------------------------------------
select /*+ rule */* from emp1 where exists (select 1 from dept1 where
dept1.deptno=emp1.deptno)

Plan hash value: 4169263234

------------------------------------
| Id  | Operation          | Name  |
------------------------------------
|   0 | SELECT STATEMENT   |       |
|*  1 |  FILTER            |       |
|   2 |   TABLE ACCESS FULL| EMP1  |
|*  3 |   TABLE ACCESS FULL| DEPT1 |
------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

1 - filter( IS NOT NULL)
3 - filter("DEPT1"."DEPTNO"=:B1)

Note
-----
- rule based optimizer used (consider using cbo)

/*

会用emp1的值去匹配dept1中是否有此值，对dept1会有大量的扫描

dept1 的deptno 字段有索引+ emp1的值比较少 适合用此方法

*/

5.存在主外键+CBO in操作的执行计划

select * from emp where emp.deptno in (select deptno from dept)  --9hs3bpna0nun4
--============================================
SQL_ID  9hs3bpna0nun4, child number 0
-------------------------------------
select * from emp where emp.deptno in (select deptno from dept)

Plan hash value: 3956160932

--------------------------------------------------------------------------
| Id  | Operation         | Name | Rows  | Bytes | Cost (%CPU)| Time     |
--------------------------------------------------------------------------
|   0 | SELECT STATEMENT  |      |       |       |     3 (100)|          |
|*  1 |  TABLE ACCESS FULL| EMP  |    14 |   532 |     3   (0)| 00:00:01 |
--------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

1 - filter("EMP"."DEPTNO" IS NOT NULL)

/*

类似 CBO 下in操作

*/

6.CBO+主外键的 exists 操作

select * from emp where exists (select 1 from dept where dept.deptno=emp.deptno) --6t5nqxmnu0sa5
--========================================================
SQL_ID  6t5nqxmnu0sa5, child number 0
-------------------------------------
select * from emp where exists (select 1 from dept where
dept.deptno=emp.deptno)

Plan hash value: 3956160932

--------------------------------------------------------------------------
| Id  | Operation         | Name | Rows  | Bytes | Cost (%CPU)| Time     |
--------------------------------------------------------------------------
|   0 | SELECT STATEMENT  |      |       |       |     3 (100)|          |
|*  1 |  TABLE ACCESS FULL| EMP  |    14 |   532 |     3   (0)| 00:00:01 |
--------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

1 - filter("EMP"."DEPTNO" IS NOT NULL)

/*

</pre><pre name="code" class="sql">*/

7.CBO+无索引 in操作

select * from emp1 where deptno in (select deptno from dept1)  --d4gg9u75dsdd6
--==============================================================
SQL_ID  d4gg9u75dsdd6, child number 0
-------------------------------------
select * from emp1 where deptno in (select deptno from dept1)

Plan hash value: 1645276872

----------------------------------------------------------------------------
| Id  | Operation          | Name  | Rows  | Bytes | Cost (%CPU)| Time     |
----------------------------------------------------------------------------
|   0 | SELECT STATEMENT   |       |       |       |     7 (100)|          |
|*  1 |  HASH JOIN SEMI    |       |    14 |  1400 |     7  (15)| 00:00:01 |
|   2 |   TABLE ACCESS FULL| EMP1  |    14 |  1218 |     3   (0)| 00:00:01 |
|   3 |   TABLE ACCESS FULL| DEPT1 |     4 |    52 |     3   (0)| 00:00:01 |
----------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

1 - access("DEPTNO"="DEPTNO")

Note
-----
- dynamic sampling used for this statement (level=2)

/*

</pre><pre name="code" class="sql">*/

8.无索引+CBO exists操作

select * from emp1 where exists (select 1 from dept1 where dept1.deptno=emp1.deptno)  --5cxf3nqy3rctb
--==========================================================================
SQL_ID  5cxf3nqy3rctb, child number 0
-------------------------------------
select * from emp1 where exists (select 1 from dept1 where
dept1.deptno=emp1.deptno)

Plan hash value: 1645276872

----------------------------------------------------------------------------
| Id  | Operation          | Name  | Rows  | Bytes | Cost (%CPU)| Time     |
----------------------------------------------------------------------------
|   0 | SELECT STATEMENT   |       |       |       |     7 (100)|          |
|*  1 |  HASH JOIN SEMI    |       |    14 |  1400 |     7  (15)| 00:00:01 |
|   2 |   TABLE ACCESS FULL| EMP1  |    14 |  1218 |     3   (0)| 00:00:01 |
|   3 |   TABLE ACCESS FULL| DEPT1 |     4 |    52 |     3   (0)| 00:00:01 |
----------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

1 - access("DEPT1"."DEPTNO"="EMP1"."DEPTNO")

Note
-----
- dynamic sampling used for this statement (level=2)

--创建索引

CREATE INDEX EMP1_DEPTNO ON EMP1(DEPTNO)
CREATE INDEX DEPT1_DEPTNO ON DEPT1(DEPTNO)

9.有索引+RBO in操作

select /* +RULE */* from emp1 where emp1.deptno in (select deptno from dept1)  --38jnq9n32jjt4
---=====================================================
SQL_ID  38jnq9n32jjt4, child number 0
-------------------------------------
select /* +RULE */* from emp1 where emp1.deptno in (select deptno from
dept1)

Plan hash value: 4046719091

-----------------------------------------------------------------------------------
| Id  | Operation          | Name         | Rows  | Bytes | Cost (%CPU)| Time     |
-----------------------------------------------------------------------------------
|   0 | SELECT STATEMENT   |              |       |       |     3 (100)|          |
|   1 |  NESTED LOOPS SEMI |              |    14 |  1400 |     3   (0)| 00:00:01 |
|   2 |   TABLE ACCESS FULL| EMP1         |    14 |  1218 |     3   (0)| 00:00:01 |
|*  3 |   INDEX RANGE SCAN | DEPT1_DEPTNO |     4 |    52 |     0   (0)|          |
-----------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

3 - access("EMP1"."DEPTNO"="DEPTNO")

Note
-----
- dynamic sampling used for this statement (level=2)

/*

走的嵌套循环联结

*/

10.有索引+RBO exists操作

select /* +RULE */* from emp1 where exists (select 1 from dept1 where dept1.deptno=emp1.deptno)   --2uajdy6rsmgdu
--==========================================================
SQL_ID  2uajdy6rsmgdu, child number 0
-------------------------------------
select /* +RULE */* from emp1 where exists (select 1 from dept1 where
dept1.deptno=emp1.deptno)

Plan hash value: 4046719091

-----------------------------------------------------------------------------------
| Id  | Operation          | Name         | Rows  | Bytes | Cost (%CPU)| Time     |
-----------------------------------------------------------------------------------
|   0 | SELECT STATEMENT   |              |       |       |     3 (100)|          |
|   1 |  NESTED LOOPS SEMI |              |    14 |  1400 |     3   (0)| 00:00:01 |
|   2 |   TABLE ACCESS FULL| EMP1         |    14 |  1218 |     3   (0)| 00:00:01 |
|*  3 |   INDEX RANGE SCAN | DEPT1_DEPTNO |     4 |    52 |     0   (0)|          |
-----------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

3 - access("DEPT1"."DEPTNO"="EMP1"."DEPTNO")

Note
-----
- dynamic sampling used for this statement (level=2)

</pre>11.有索引+CBO in操作<p></p><p></p><pre name="code" class="sql"> select /* CHENJ */* from emp1 where emp1.deptno in (select deptno from dept1)   --0zztfa0s5agkh
SQL_ID  0zztfa0s5agkh, child number 0
-------------------------------------
select /* CHENJ */* from emp1 where emp1.deptno in (select deptno from
dept1)

Plan hash value: 4046719091

-----------------------------------------------------------------------------------
| Id  | Operation          | Name         | Rows  | Bytes | Cost (%CPU)| Time     |
-----------------------------------------------------------------------------------
|   0 | SELECT STATEMENT   |              |       |       |     3 (100)|          |
|   1 |  NESTED LOOPS SEMI |              |    14 |  1400 |     3   (0)| 00:00:01 |
|   2 |   TABLE ACCESS FULL| EMP1         |    14 |  1218 |     3   (0)| 00:00:01 |
|*  3 |   INDEX RANGE SCAN | DEPT1_DEPTNO |     4 |    52 |     0   (0)|          |
-----------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

3 - access("EMP1"."DEPTNO"="DEPTNO")

Note
-----
- dynamic sampling used for this statement (level=2)

12.有索引+CBO exists操作

select /* CHENJ */* from emp1 where exists (select 1 from dept1 where dept1.deptno=emp1.deptno)   --gq143uhy91jy6
SQL_ID  gq143uhy91jy6, child number 0
-------------------------------------
select /* CHENJ */* from emp1 where exists (select 1 from dept1 where
dept1.deptno=emp1.deptno)

Plan hash value: 4046719091

-----------------------------------------------------------------------------------
| Id  | Operation          | Name         | Rows  | Bytes | Cost (%CPU)| Time     |
-----------------------------------------------------------------------------------
|   0 | SELECT STATEMENT   |              |       |       |     3 (100)|          |
|   1 |  NESTED LOOPS SEMI |              |    14 |  1400 |     3   (0)| 00:00:01 |
|   2 |   TABLE ACCESS FULL| EMP1         |    14 |  1218 |     3   (0)| 00:00:01 |
|*  3 |   INDEX RANGE SCAN | DEPT1_DEPTNO |     4 |    52 |     0   (0)|          |
-----------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

3 - access("DEPT1"."DEPTNO"="EMP1"."DEPTNO")

Note
-----
- dynamic sampling used for this statement (level=2)

不完全结论：测试数据+一些条件限制可能不完善，但是初步结论用CBO优化器时，in 与 exists 最后的执行计划并无太大区别

RBO优化器时，in 与 exists 要看具体应用场景了