Oracle执行计划filter下多个节点的优化

FILTER操作是执行计划中常见的操作，这种操作有两种情况：

l 只有一个子节点，那么就是简单过滤操作。

l有多个子节点，那么就是类似NESTED LOOPS操作，只不过与NESTED LOOPS差别在于，FILTER内部会构建HASH表，对于重复匹配的，不会再次进行循环查找，而是利用已有结果，提高效率。但是一旦重复匹配的较少，循环次数多，那么，FILTER操作将是严重影响性能的操作，可能你的SQL几天都执行不完了。

真题1、执行计划里的access和filter有什么区别？

答案：如下所示：

Predicate Information (identified by operation id):

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

4 - access("A"."EMPNO"="B"."MGR")

filter("A"."EMPNO"="B"."MGR")

5 - filter("B"."MGR" IS NOT NULL)

一般而言，access表示这个谓词条件的值将会影响数据的访问路径（表还是索引）；filter表示谓词条件的值不会影响数据的访问路劲，只起到过滤的作用。NOT IN或MIN函数等容易产生filter操作。

对于filter而言如果只有一个子节点，那么就是简单过滤操作（独立操作）。如果有两个或更多子节点，那么就是类似Nested Loops操作，只不过与Nested Loops差别在于，filter内部会构建HASH表，对于重复匹配的，不会再次进行循环查找，而是利用已有结果，提高效率。但是一旦重复匹配的较少，循环次数多，那么，filter操作将是严重影响性能的操作，可能会导致目标SQL几天都执行不完。

下面看看各种情况下的FILTER操作：

（一）单子节点：

LHR@orclasm > set autot on

LHR@orclasm > SELECT T.JOB, COUNT(1) FROM SCOTT.EMP T GROUP BY T.JOB  HAVING COUNT(1)>3;

JOB         COUNT(1)

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

CLERK              4

SALESMAN           4

Execution Plan

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

Plan hash value: 2138686577

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

| Id  | Operation           | Name | Rows  | Bytes | Cost (%CPU)| Time     |

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

|   0 | SELECT STATEMENT    |      |     1 |     8 |     4  (25)| 00:00:01 |

|*  1 |  FILTER             |      |       |       |            |          |

|   2 |   HASH GROUP BY     |      |     1 |     8 |     4  (25)| 00:00:01 |

|   3 |    TABLE ACCESS FULL| EMP  |    14 |   112 |     3   (0)| 00:00:01 |

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

Predicate Information (identified by operation id):

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

1 - filter(COUNT(*)>3)

Statistics

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

25  recursive calls

4  db block gets

6  consistent gets

0  physical reads

1544  redo size

660  bytes sent via SQL*Net to client

519  bytes received via SQL*Net from client

2  SQL*Net roundtrips to/from client

0  sorts (memory)

0  sorts (disk)

2  rows processed

很显然ID1的filter操作只有一个子节点ID2，在这种情况下的filter操作也就是单纯的过滤操作。

（二）多子节点：

filter多子节点往往就是性能杀手，主要出现在子查询无法UNNEST查询转换，经常遇到的情况就是NOT IN子查询、子查询和OR连用、复杂子查询等情况。

避免使用复杂的集合函数，像NOT IN等。通常，要避免在索引列上使用NOT，NOT会产生和在索引列上使用函数相同的影响。当Oracle遇到NOT操作符时，它就会停止使用索引转而执行全表扫描。很多时候用EXISTS和NOT EXISTS代替IN和NOT IN语句是一个好的选择。需要注意的是，在Oracle 11g之前，若NOT IN的列没有指定非空的话（注意：是主表和子表的列未同时有NOT NULL约束，或都未加IS NOT NULL限制），则NOT IN选择的是filter操作（如果指定了非空，那么会选择ANTI的反连接），但是从Oracle 11g开始有新的ANTI NA（NULL AWARE）优化，可以对子查询进行UNNEST，NOT IN和NOT EXISTS都选择的是ANTI的反连接，所以效率是一样的。在一般情况下，ANTI的反连接算法比filter更高效。对于未UNNEST的子查询，若选择了filter操作，则至少有两个子节点，执行计划还有个特点就是Predicate谓词部分有“:B1”这种类似绑定变量的内容，内部操作走类似Nested Loops操作。如果在Oracle 11g之前，遇到NOT IN无法UNNEST，那么可以将NOT IN部分的匹配条件均设为NOT NULL约束。若不添加NOT NULL约束，则需要两个条件均增加IS NOT NULL条件。当然也可以将NOT IN修改为NOT EXISTS。

分别在Oracle 10g和Oracle 11g实验：

SELECT * FROM V$VERSION;

DROP TABLE EMP PURGE;

DROP TABLE DEPT PURGE;

CREATE TABLE EMP AS SELECT * FROM SCOTT.EMP;

CREATE TABLE DEPT AS SELECT * FROM SCOTT.DEPT;

SET TIMING ON

SET LINESIZE 1000

SET AUTOTRACE TRACEONLY

--写法1

SELECT * FROM DEPT WHERE DEPTNO NOT IN (SELECT DEPTNO FROM EMP);

--写法2

SELECT * FROM DEPT WHERE NOT EXISTS (SELECT DEPTNO FROM EMP WHERE EMP.DEPTNO=DEPT.DEPTNO);

--写法3

SELECT * FROM DEPT WHERE DEPTNO NOT IN (SELECT DEPTNO FROM EMP WHERE DEPTNO IS NOT NULL) AND DEPTNO IS NOT NULL;

--写法4

SELECT * FROM DEPT WHERE DEPTNO NOT IN (SELECT DEPTNO FROM EMP) AND DEPTNO IS NOT NULL;

--写法5

SELECT * FROM DEPT WHERE DEPTNO NOT IN (SELECT DEPTNO FROM EMP WHERE DEPTNO IS NOT NULL);

其结果如下表所示：

版本

SQL语句

操作

逻辑读

执行计划

Oracle 10g

SELECT * FROM DEPT WHERE DEPTNO NOT IN (SELECT DEPTNO FROM EMP);

FILTER

15

|--------------------------------------------------------------------------

| Id  | Operation          | Name | Rows  | Bytes | Cost (%CPU)| Time     |

|--------------------------------------------------------------------------

|   0 | SELECT STATEMENT   |      |     1 |    30 |     4   (0)| 00:00:01 |

|*  1 |  FILTER            |      |       |       |            |          |

|   2 |   TABLE ACCESS FULL| DEPT |     4 |   120 |     2   (0)| 00:00:01 |

|*  3 |   TABLE ACCESS FULL| EMP  |    13 |   169 |     2   (0)| 00:00:01 |

|--------------------------------------------------------------------------

SELECT * FROM DEPT WHERE NOT EXISTS (SELECT DEPTNO FROM EMP WHERE EMP.DEPTNO=DEPT.DEPTNO);

HASH JOIN ANTI

6

|---------------------------------------------------------------------------

| Id  | Operation          | Name | Rows  | Bytes | Cost (%CPU)| Time     |

|---------------------------------------------------------------------------

|   0 | SELECT STATEMENT   |      |     1 |    43 |     5  (20)| 00:00:01 |

|*  1 |  HASH JOIN ANTI    |      |     1 |    43 |     5  (20)| 00:00:01 |

|   2 |   TABLE ACCESS FULL| DEPT |     4 |   120 |     2   (0)| 00:00:01 |

|   3 |   TABLE ACCESS FULL| EMP  |    14 |   182 |     2   (0)| 00:00:01 |

|---------------------------------------------------------------------------

SELECT * FROM DEPT WHERE DEPTNO NOT IN (SELECT DEPTNO FROM EMP WHERE DEPTNO IS NOT NULL) AND DEPTNO IS NOT NULL;

HASH JOIN ANTI

6

|---------------------------------------------------------------------------

| Id  | Operation          | Name | Rows  | Bytes | Cost (%CPU)| Time     |

|---------------------------------------------------------------------------

|   0 | SELECT STATEMENT   |      |     1 |    43 |     5  (20)| 00:00:01 |

|*  1 |  HASH JOIN ANTI    |      |     1 |    43 |     5  (20)| 00:00:01 |

|*  2 |   TABLE ACCESS FULL| DEPT |     4 |   120 |     2   (0)| 00:00:01 |

|*  3 |   TABLE ACCESS FULL| EMP  |    14 |   182 |     2   (0)| 00:00:01 |

|---------------------------------------------------------------------------

SELECT * FROM DEPT WHERE DEPTNO NOT IN (SELECT DEPTNO FROM EMP) AND DEPTNO IS NOT NULL;

FILTER

15

|---------------------------------------------------------------------------

| Id  | Operation          | Name | Rows  | Bytes | Cost (%CPU)| Time     |

|---------------------------------------------------------------------------

|   0 | SELECT STATEMENT   |      |     2 |    60 |     6   (0)| 00:00:01 |

|*  1 |  FILTER            |      |       |       |            |          |

|*  2 |   TABLE ACCESS FULL| DEPT |     4 |   120 |     2   (0)| 00:00:01 |

|*  3 |   TABLE ACCESS FULL| EMP  |    13 |   169 |     2   (0)| 00:00:01 |

|---------------------------------------------------------------------------

SELECT * FROM DEPT WHERE DEPTNO NOT IN (SELECT DEPTNO FROM EMP WHERE DEPTNO IS NOT NULL);

FILTER

15

|---------------------------------------------------------------------------

| Id  | Operation          | Name | Rows  | Bytes | Cost (%CPU)| Time     |

|---------------------------------------------------------------------------

|   0 | SELECT STATEMENT   |      |     1 |    30 |     4   (0)| 00:00:01 |

|*  1 |  FILTER            |      |       |       |            |          |

|   2 |   TABLE ACCESS FULL| DEPT |     4 |   120 |     2   (0)| 00:00:01 |

|*  3 |   TABLE ACCESS FULL| EMP  |    13 |   169 |     2   (0)| 00:00:01 |

|---------------------------------------------------------------------------

Oracle 11g

SELECT * FROM DEPT WHERE DEPTNO NOT IN (SELECT DEPTNO FROM EMP);

HASH JOIN ANTI NA

6

|---------------------------------------------------------------------------

| Id  | Operation          | Name | Rows  | Bytes | Cost (%CPU)| Time     |

|---------------------------------------------------------------------------

|   0 | SELECT STATEMENT   |      |     4 |   172 |     5  (20)| 00:00:01 |

|*  1 |  HASH JOIN ANTI NA |      |     4 |   172 |     5  (20)| 00:00:01 |

|   2 |   TABLE ACCESS FULL| DEPT |     4 |   120 |     2   (0)| 00:00:01 |

|   3 |   TABLE ACCESS FULL| EMP  |    12 |   156 |     2   (0)| 00:00:01 |

|---------------------------------------------------------------------------

SELECT * FROM DEPT WHERE NOT EXISTS (SELECT DEPTNO FROM EMP WHERE EMP.DEPTNO=DEPT.DEPTNO);

HASH JOIN ANTI

6

|---------------------------------------------------------------------------

| Id  | Operation          | Name | Rows  | Bytes | Cost (%CPU)| Time     |

|---------------------------------------------------------------------------

|   0 | SELECT STATEMENT   |      |     4 |   172 |     5  (20)| 00:00:01 |

|*  1 |  HASH JOIN ANTI    |      |     4 |   172 |     5  (20)| 00:00:01 |

|   2 |   TABLE ACCESS FULL| DEPT |     4 |   120 |     2   (0)| 00:00:01 |

|   3 |   TABLE ACCESS FULL| EMP  |    12 |   156 |     2   (0)| 00:00:01 |

|---------------------------------------------------------------------------

SELECT * FROM DEPT WHERE DEPTNO NOT IN (SELECT DEPTNO FROM EMP WHERE DEPTNO IS NOT NULL) AND DEPTNO IS NOT NULL;

HASH JOIN ANTI

6

|---------------------------------------------------------------------------

| Id  | Operation          | Name | Rows  | Bytes | Cost (%CPU)| Time     |

|---------------------------------------------------------------------------

|   0 | SELECT STATEMENT   |      |     4 |   172 |     5  (20)| 00:00:01 |

|*  1 |  HASH JOIN ANTI    |      |     4 |   172 |     5  (20)| 00:00:01 |

|*  2 |   TABLE ACCESS FULL| DEPT |     4 |   120 |     2   (0)| 00:00:01 |

|*  3 |   TABLE ACCESS FULL| EMP  |    12 |   156 |     2   (0)| 00:00:01 |

|---------------------------------------------------------------------------

SELECT * FROM DEPT WHERE DEPTNO NOT IN (SELECT DEPTNO FROM EMP) AND DEPTNO IS NOT NULL;

HASH JOIN ANTI SNA

6

|---------------------------------------------------------------------------

| Id  | Operation          | Name | Rows  | Bytes | Cost (%CPU)| Time     |

|---------------------------------------------------------------------------

|   0 | SELECT STATEMENT   |      |     4 |   172 |     5  (20)| 00:00:01 |

|*  1 |  HASH JOIN ANTI SNA|      |     4 |   172 |     5  (20)| 00:00:01 |

|   2 |   TABLE ACCESS FULL| DEPT |     4 |   120 |     2   (0)| 00:00:01 |

|*  3 |   TABLE ACCESS FULL| EMP  |    12 |   156 |     2   (0)| 00:00:01 |

|---------------------------------------------------------------------------

SELECT * FROM DEPT WHERE DEPTNO NOT IN (SELECT DEPTNO FROM EMP WHERE DEPTNO IS NOT NULL);

HASH JOIN ANTI NA

6

|---------------------------------------------------------------------------

| Id  | Operation          | Name | Rows  | Bytes | Cost (%CPU)| Time     |

|---------------------------------------------------------------------------

|   0 | SELECT STATEMENT   |      |     4 |   172 |     5  (20)| 00:00:01 |

|*  1 |  HASH JOIN ANTI NA |      |     4 |   172 |     5  (20)| 00:00:01 |

|*  2 |   TABLE ACCESS FULL| DEPT |     4 |   120 |     2   (0)| 00:00:01 |

|   3 |   TABLE ACCESS FULL| EMP  |    12 |   156 |     2   (0)| 00:00:01 |

|---------------------------------------------------------------------------

看一下详细执行计划：

SELECT * FROM V$VERSION;

DROP TABLE EMP PURGE;

DROP TABLE DEPT PURGE;

CREATE TABLE EMP AS SELECT * FROM SCOTT.EMP;

CREATE TABLE DEPT AS SELECT * FROM SCOTT.DEPT;

SET TIMING ON

SET LINESIZE 1000

SET AUTOTRACE TRACEONLY

--写法1

SELECT /*+optimizer_features_enable('10.2.0.5')*/ * FROM DEPT WHERE DEPTNO NOT IN (SELECT DEPTNO FROM EMP);

SELECT * FROM DEPT WHERE DEPTNO NOT IN (SELECT DEPTNO FROM EMP);

LHR@orclasm > SELECT /*+optimizer_features_enable('10.2.0.5')*/ * FROM DEPT WHERE DEPTNO NOT IN (SELECT DEPTNO FROM EMP);

DEPTNO DNAME          LOC

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

40 OPERATIONS     BOSTON

Execution Plan

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

Plan hash value: 3547749009

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

| Id  | Operation          | Name | Rows  | Bytes | Cost (%CPU)| Time     |

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

|   0 | SELECT STATEMENT   |      |     1 |    30 |     5   (0)| 00:00:01 |

|*  1 |  FILTER            |      |       |       |            |          |

|   2 |   TABLE ACCESS FULL| DEPT |     4 |   120 |     3   (0)| 00:00:01 |

|*  3 |   TABLE ACCESS FULL| EMP  |    13 |   169 |     2   (0)| 00:00:01 |

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

Predicate Information (identified by operation id):

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

1 - filter( NOT EXISTS (SELECT 0 FROM "EMP" "EMP" WHERE

LNNVL("DEPTNO"<>:B1)))

3 - filter(LNNVL("DEPTNO"<>:B1))

Note

-----

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

Statistics

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

15  recursive calls

0  db block gets

31  consistent gets

0  physical reads

0  redo size

674  bytes sent via SQL*Net to client

519  bytes received via SQL*Net from client

2  SQL*Net roundtrips to/from client

0  sorts (memory)

0  sorts (disk)

1  rows processed

LHR@orclasm > SELECT * FROM DEPT WHERE DEPTNO NOT IN (SELECT DEPTNO FROM EMP);

DEPTNO DNAME          LOC

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

40 OPERATIONS     BOSTON

Execution Plan

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

Plan hash value: 2100826622

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

| Id  | Operation          | Name | Rows  | Bytes | Cost (%CPU)| Time     |

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

|   0 | SELECT STATEMENT   |      |     4 |   172 |     7  (15)| 00:00:01 |

|*  1 |  HASH JOIN ANTI NA |      |     4 |   172 |     7  (15)| 00:00:01 |

|   2 |   TABLE ACCESS FULL| DEPT |     4 |   120 |     3   (0)| 00:00:01 |

|   3 |   TABLE ACCESS FULL| EMP  |    14 |   182 |     3   (0)| 00:00:01 |

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

Predicate Information (identified by operation id):

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

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

Note

-----

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

Statistics

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

7  recursive calls

0  db block gets

14  consistent gets

0  physical reads

0  redo size

674  bytes sent via SQL*Net to client

519  bytes received via SQL*Net from client

2  SQL*Net roundtrips to/from client

0  sorts (memory)

0  sorts (disk)

1  rows processed

针对上面的NOT IN子查询，如果子查询中的DEPTNO有NULL存在，那么整个查询都不会有结果，在Oracle 11g之前，如果主表和子表的DEPTNO未同时有NOT NULL约束，或都未加IS NOT NULL限制，那么Oracle会选择filter。从Oracle 11g开始有新的ANTI NA（NULL AWARE）优化，可以对子查询进行UNNEST，从而提高效率。对于未UNNEST的子查询，若选择了FILTER操作，则至少有两个子节点，执行计划还有个特点就是Predicate谓词部分有“:B1”这种类似绑定变量的内容，内部操作走类似Nested Loops操作。

如下所示：

LHR@orclasm > SELECT  /*+rule gather_plan_statistics*/  *

2    FROM SCOTT.EMP

3   WHERE NOT EXISTS (SELECT 0

4            FROM SCOTT.DEPT

5           WHERE DEPT.DNAME = 'SALES'

6             AND DEPT.DEPTNO = EMP.DEPTNO)

7     AND NOT EXISTS

8   (SELECT 0 FROM SCOTT.BONUS WHERE BONUS.ENAME = EMP.ENAME);

EMPNO ENAME      JOB              MGR HIREDATE                   SAL       COMM     DEPTNO

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

7369 SMITH      CLERK           7902 1980-12-17 00:00:00        800                    20

7566 JONES      MANAGER         7839 1981-04-02 00:00:00       2975                    20

7782 CLARK      MANAGER         7839 1981-06-09 00:00:00       2450                    10

7788 SCOTT      ANALYST         7566 1987-04-19 00:00:00       3000                    20

7839 KING       PRESIDENT            1981-11-17 00:00:00       5000                    10

7876 ADAMS      CLERK           7788 1987-05-23 00:00:00       1100                    20

7902 FORD       ANALYST         7566 1981-12-03 00:00:00       3000                    20

7934 MILLER     CLERK           7782 1982-01-23 00:00:00       1300                    10

8 rows selected.

LHR@orclasm > SELECT * FROM TABLE(DBMS_XPLAN.DISPLAY_CURSOR(NULL,NULL,'ADVANCED ALLSTATS LAST PEEKED_BINDS'));

PLAN_TABLE_OUTPUT

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

SQL_ID  b8w1s38hqtjkj, child number 0

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

SELECT  /*+rule gather_plan_statistics*/  *   FROM SCOTT.EMP  WHERE NOT

EXISTS (SELECT 0           FROM SCOTT.DEPT          WHERE DEPT.DNAME =

'SALES'            AND DEPT.DEPTNO = EMP.DEPTNO)    AND NOT EXISTS

(SELECT 0 FROM SCOTT.BONUS WHERE BONUS.ENAME = EMP.ENAME)

Plan hash value: 1445856646

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

| Id  | Operation                    | Name    | Starts | A-Rows |   A-Time   | Buffers |

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

|   0 | SELECT STATEMENT             |         |      1 |      8 |00:00:00.01 |      14 |

|*  1 |  FILTER                      |         |      1 |      8 |00:00:00.01 |      14 |

|   2 |   TABLE ACCESS FULL          | EMP     |      1 |     14 |00:00:00.01 |       8 |

|*  3 |   TABLE ACCESS BY INDEX ROWID| DEPT    |      3 |      1 |00:00:00.01 |       6 |

|*  4 |    INDEX UNIQUE SCAN         | PK_DEPT |      3 |      3 |00:00:00.01 |       3 |

|*  5 |   TABLE ACCESS FULL          | BONUS   |      8 |      0 |00:00:00.01 |       0 |

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

Query Block Name / Object Alias (identified by operation id):

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

1 - SEL$1

2 - SEL$1 / EMP@SEL$1

3 - SEL$2 / DEPT@SEL$2

4 - SEL$2 / DEPT@SEL$2

5 - SEL$3 / BONUS@SEL$3

Outline Data

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

/*+

BEGIN_OUTLINE_DATA

IGNORE_OPTIM_EMBEDDED_HINTS

OPTIMIZER_FEATURES_ENABLE('11.2.0.3')

DB_VERSION('11.2.0.3')

RBO_OUTLINE

OUTLINE_LEAF(@"SEL$2")

OUTLINE_LEAF(@"SEL$3")

OUTLINE_LEAF(@"SEL$1")

FULL(@"SEL$1" "EMP"@"SEL$1")

FULL(@"SEL$3" "BONUS"@"SEL$3")

INDEX_RS_ASC(@"SEL$2" "DEPT"@"SEL$2" ("DEPT"."DEPTNO"))

END_OUTLINE_DATA

*/

Predicate Information (identified by operation id):

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

1 - filter(( IS NULL AND  IS NULL))

3 - filter("DEPT"."DNAME"='SALES')

4 - access("DEPT"."DEPTNO"=:B1)

5 - filter("BONUS"."ENAME"=:B1)

Column Projection Information (identified by operation id):

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

1 - "EMP"."EMPNO"[NUMBER,22], "EMP"."ENAME"[VARCHAR2,10],

"EMP"."JOB"[VARCHAR2,9], "EMP"."MGR"[NUMBER,22], "EMP"."HIREDATE"[DATE,7],

"EMP"."SAL"[NUMBER,22], "EMP"."COMM"[NUMBER,22], "EMP"."DEPTNO"[NUMBER,22]

2 - "EMP"."EMPNO"[NUMBER,22], "EMP"."ENAME"[VARCHAR2,10],

"EMP"."JOB"[VARCHAR2,9], "EMP"."MGR"[NUMBER,22], "EMP"."HIREDATE"[DATE,7],

"EMP"."SAL"[NUMBER,22], "EMP"."COMM"[NUMBER,22], "EMP"."DEPTNO"[NUMBER,22]

4 - "DEPT".ROWID[ROWID,10]

Note

-----

- rule based optimizer used (consider using cbo)

70 rows selected.

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

| Id  | Operation                    | Name    | Starts | A-Rows |   A-Time   | Buffers |

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

|   0 | SELECT STATEMENT             |         |      1 |      8 |00:00:00.01 |      14 |

|*  1 |  FILTER                      |         |      1 |      8 |00:00:00.01 |      14 |

|   2 |   TABLE ACCESS FULL          | EMP     |      1 |     14 |00:00:00.01 |       8 |

|*  3 |   TABLE ACCESS BY INDEX ROWID| DEPT    |      3 |      1 |00:00:00.01 |       6 |

|*  4 |    INDEX UNIQUE SCAN         | PK_DEPT |      3 |      3 |00:00:00.01 |       3 |

|*  5 |   TABLE ACCESS FULL          | BONUS   |      8 |      0 |00:00:00.01 |       0 |

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

Predicate Information (identified by operation id):

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

1 - filter(( IS NULL AND  IS NULL))

3 - filter("DEPT"."DNAME"='SALES')

4 - access("DEPT"."DEPTNO"=:B1)

5 - filter("BONUS"."ENAME"=:B1)

该执行计划的执行顺序为：

①　ID1有3个子节点ID2、ID3、ID5，由于ID2最小，故先执行ID2；

②　ID2对EMP表进行全表扫描，将返回14行给ID1；

③　在相关组合中ID2应当控制ID3和ID5的执行，由于Oracle此处对Distinct Value做了优化，所以ID3只执行了3次。

④　ID4执行3次，并返回3个RWOID到ID3；

⑤　ID3使用ID4返回的3个ROWID来访问数据表块，过滤“filter("DEPT"."DNAME"='SALES')”的数据，由于是NOT EXISTS，所以这导致ID1原来获得的14行排除6行的“"DEPT"."DNAME"='SALES'”，只剩下8行，这8行数据影响了ID5的执行次数，将执行8次，其中“filter("BONUS"."ENAME"=:B1)”过滤条件的“:B1”由ID1的8行数据提供，ID5没有返回数据，所以那8行没有减少ID1将8行彻底过滤的数据返回给客户端。

filter多子节点往往就是性能杀手，主要出现在子查询无法UNNEST查询转换，经常遇到的情况就是NOT IN子查询、子查询和OR连用、复杂子查询等情况。

DROP TABLE T_20170703_LHR_01 PURGE;

DROP TABLE T_20170703_LHR_02 PURGE;

DROP TABLE T_20170703_LHR_03 PURGE;

CREATE TABLE T_20170703_LHR_01 AS SELECT OBJECT_ID,OBJECT_NAME,OBJECT_TYPE FROM DBA_OBJECTS;

CREATE TABLE T_20170703_LHR_02 AS SELECT OBJECT_ID,OBJECT_NAME FROM USER_OBJECTS;

CREATE TABLE T_20170703_LHR_03 AS SELECT OBJECT_ID,OBJECT_NAME FROM USER_OBJECTS WHERE ROWNUM <=1000;

CREATE INDEX IND_T1_OBJ_ID_1 ON T_20170703_LHR_01(OBJECT_ID);

CREATE INDEX IND_T2_OBJ_ID_1 ON T_20170703_LHR_02(OBJECT_ID);

CREATE INDEX IND_T3_OBJ_ID_1 ON T_20170703_LHR_03(OBJECT_ID);

EXEC DBMS_STATS.GATHER_TABLE_STATS(USER,'t_20170703_LHR_01');

EXEC DBMS_STATS.GATHER_TABLE_STATS(USER,'t_20170703_LHR_02');

EXEC DBMS_STATS.GATHER_TABLE_STATS(USER,'t_20170703_LHR_03');

ALTER SESSION SET STATISTICS_LEVEL=ALL;

SELECT COUNT(1)

FROM T_20170703_LHR_01   T1

WHERE T1.OBJECT_TYPE = 'TABLE'

OR EXISTS (SELECT 1 FROM T_20170703_LHR_02 T2 WHERE T1.OBJECT_ID = T2.OBJECT_ID)

OR EXISTS (SELECT 1 FROM T_20170703_LHR_03 T3 WHERE T1.OBJECT_ID = T3.OBJECT_ID);

SELECT * FROM TABLE(DBMS_XPLAN.DISPLAY_CURSOR(NULL,NULL,'allstats last'));

SELECT COUNT(1)

FROM (SELECT T1.*

FROM T_20170703_LHR_01 T1

WHERE T1.OBJECT_TYPE = 'TABLE'

UNION ALL (SELECT T1.*

FROM T_20170703_LHR_01 T1, T_20170703_LHR_02 T2

WHERE T1.OBJECT_ID = T2.OBJECT_ID

AND T1.OBJECT_TYPE <> 'TABLE'

UNION

SELECT T1.*

FROM T_20170703_LHR_01 T1, T_20170703_LHR_03 T3

WHERE T1.OBJECT_ID = T3.OBJECT_ID

AND T1.OBJECT_TYPE <> 'TABLE'));

SELECT * FROM TABLE(DBMS_XPLAN.DISPLAY_CURSOR(NULL,NULL,'allstats last'));

WITH TMP_T1 AS

(SELECT T1.* FROM T_20170703_LHR_01 T1)

SELECT COUNT(1)

FROM (SELECT T1.*

FROM TMP_T1 T1

WHERE T1.OBJECT_TYPE = 'TABLE'

UNION ALL (SELECT T1.*

FROM TMP_T1 T1, T_20170703_LHR_02 T2

WHERE T1.OBJECT_ID = T2.OBJECT_ID

AND T1.OBJECT_TYPE <> 'TABLE'

UNION

SELECT T1.*

FROM TMP_T1 T1, T_20170703_LHR_03 T3

WHERE T1.OBJECT_ID = T3.OBJECT_ID

AND T1.OBJECT_TYPE <> 'TABLE'));

SELECT * FROM TABLE(DBMS_XPLAN.DISPLAY_CURSOR(NULL,NULL,'allstats last'));

具体执行计划：

LHR@orclasm > ALTER SESSION SET STATISTICS_LEVEL=ALL;

Session altered.

LHR@orclasm > SELECT COUNT(1)

2    FROM T_20170703_LHR_01   T1

3   WHERE T1.OBJECT_TYPE = 'TABLE'

4      OR EXISTS (SELECT 1 FROM T_20170703_LHR_02 T2 WHERE T1.OBJECT_ID = T2.OBJECT_ID)

5      OR EXISTS (SELECT 1 FROM T_20170703_LHR_03 T3 WHERE T1.OBJECT_ID = T3.OBJECT_ID);

COUNT(1)

----------

5060

LHR@orclasm > SELECT * FROM TABLE(DBMS_XPLAN.DISPLAY_CURSOR(NULL,NULL,'allstats last'));

PLAN_TABLE_OUTPUT

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

SQL_ID  5894cbw5v4mpj, child number 0

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

SELECT COUNT(1)   FROM T_20170703_LHR_01   T1  WHERE T1.OBJECT_TYPE =

'TABLE'     OR EXISTS (SELECT 1 FROM T_20170703_LHR_02 T2 WHERE

T1.OBJECT_ID = T2.OBJECT_ID)     OR EXISTS (SELECT 1 FROM

T_20170703_LHR_03 T3 WHERE T1.OBJECT_ID = T3.OBJECT_ID)

Plan hash value: 1566256780

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

| Id  | Operation           | Name              | Starts | E-Rows | A-Rows |   A-Time   | Buffers |

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

|   0 | SELECT STATEMENT    |                   |      1 |        |      1 |00:00:00.17 |     149K|

|   1 |  SORT AGGREGATE     |                   |      1 |      1 |      1 |00:00:00.17 |     149K|

|*  2 |   FILTER            |                   |      1 |        |   5060 |00:00:00.17 |     149K|

|   3 |    TABLE ACCESS FULL| T_20170703_LHR_01 |      1 |  78271 |  78271 |00:00:00.01 |     469 |

|*  4 |    INDEX RANGE SCAN | IND_T2_OBJ_ID_1   |  74941 |      1 |   1741 |00:00:00.05 |   75356 |

|*  5 |    INDEX RANGE SCAN | IND_T3_OBJ_ID_1   |  73200 |      1 |      0 |00:00:00.05 |   73308 |

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

Predicate Information (identified by operation id):

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

2 - filter(("T1"."OBJECT_TYPE"='TABLE' OR  IS NOT NULL OR  IS NOT NULL))

4 - access("T2"."OBJECT_ID"=:B1)

5 - access("T3"."OBJECT_ID"=:B1)

27 rows selected.

LHR@orclasm >

LHR@orclasm >

LHR@orclasm > SELECT COUNT(1)

2    FROM (SELECT T1.*

3            FROM T_20170703_LHR_01 T1

4           WHERE T1.OBJECT_TYPE = 'TABLE'

5          UNION ALL (SELECT T1.*

6                      FROM T_20170703_LHR_01 T1, T_20170703_LHR_02 T2

7                     WHERE T1.OBJECT_ID = T2.OBJECT_ID

8                       AND T1.OBJECT_TYPE <> 'TABLE'

9                    UNION

10                    SELECT T1.*

11                      FROM T_20170703_LHR_01 T1, T_20170703_LHR_03 T3

12                     WHERE T1.OBJECT_ID = T3.OBJECT_ID

13                       AND T1.OBJECT_TYPE <> 'TABLE'));

COUNT(1)

----------

5060

LHR@orclasm > SELECT * FROM TABLE(DBMS_XPLAN.DISPLAY_CURSOR(NULL,NULL,'allstats last'));

PLAN_TABLE_OUTPUT

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

SQL_ID  5n0xpnt0gzb0d, child number 0

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

SELECT COUNT(1)   FROM (SELECT T1.*           FROM T_20170703_LHR_01 T1

WHERE T1.OBJECT_TYPE = 'TABLE'         UNION ALL (SELECT T1.*

FROM T_20170703_LHR_01 T1, T_20170703_LHR_02 T2

WHERE T1.OBJECT_ID = T2.OBJECT_ID

AND T1.OBJECT_TYPE <> 'TABLE'                   UNION

SELECT T1.*                     FROM T_20170703_LHR_01 T1,

T_20170703_LHR_03 T3                    WHERE T1.OBJECT_ID =

T3.OBJECT_ID                      AND T1.OBJECT_TYPE <> 'TABLE'))

Plan hash value: 3651740877

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

| Id  | Operation                  | Name              | Starts | E-Rows | A-Rows |   A-Time   | Buffers |  OMem |  1Mem | Used-Mem |

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

|   0 | SELECT STATEMENT           |                   |      1 |        |      1 |00:00:00.05 |    1423 |       |       |          |

|   1 |  SORT AGGREGATE            |                   |      1 |      1 |      1 |00:00:00.05 |    1423 |       |       |          |

|   2 |   VIEW                     |                   |      1 |   4641 |   5060 |00:00:00.05 |    1423 |       |       |          |

|   3 |    UNION-ALL               |                   |      1 |        |   5060 |00:00:00.05 |    1423 |       |       |          |

|*  4 |     TABLE ACCESS FULL      | T_20170703_LHR_01 |      1 |   1631 |   3319 |00:00:00.01 |     469 |       |       |          |

|   5 |     SORT UNIQUE            |                   |      1 |   4641 |   1741 |00:00:00.05 |     954 |   178K|   178K|  158K (0)|

|   6 |      UNION-ALL             |                   |      1 |        |   2634 |00:00:00.05 |     954 |       |       |          |

|*  7 |       HASH JOIN            |                   |      1 |   2010 |   1741 |00:00:00.03 |     479 |  1452K|  1452K| 1667K (0)|

|   8 |        INDEX FAST FULL SCAN| IND_T2_OBJ_ID_1   |      1 |   2012 |   2010 |00:00:00.01 |      10 |       |       |          |

|*  9 |        TABLE ACCESS FULL   | T_20170703_LHR_01 |      1 |  76640 |  74952 |00:00:00.01 |     469 |       |       |          |

|* 10 |       HASH JOIN            |                   |      1 |   1000 |    893 |00:00:00.02 |     475 |  1452K|  1452K| 1571K (0)|

|  11 |        INDEX FAST FULL SCAN| IND_T3_OBJ_ID_1   |      1 |   1000 |   1000 |00:00:00.01 |       6 |       |       |          |

|* 12 |        TABLE ACCESS FULL   | T_20170703_LHR_01 |      1 |  76640 |  74952 |00:00:00.01 |     469 |       |       |          |

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

Predicate Information (identified by operation id):

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

4 - filter("T1"."OBJECT_TYPE"='TABLE')

7 - access("T1"."OBJECT_ID"="T2"."OBJECT_ID")

9 - filter("T1"."OBJECT_TYPE"<>'TABLE')

10 - access("T1"."OBJECT_ID"="T3"."OBJECT_ID")

12 - filter("T1"."OBJECT_TYPE"<>'TABLE')

40 rows selected.

LHR@orclasm >

LHR@orclasm >

LHR@orclasm >

LHR@orclasm > WITH TMP_T1 AS

2   (SELECT T1.* FROM T_20170703_LHR_01 T1)

3  SELECT COUNT(1)

4    FROM (SELECT T1.*

5            FROM TMP_T1 T1

6           WHERE T1.OBJECT_TYPE = 'TABLE'

7          UNION ALL (SELECT T1.*

8                      FROM TMP_T1 T1, T_20170703_LHR_02 T2

9                     WHERE T1.OBJECT_ID = T2.OBJECT_ID

10                       AND T1.OBJECT_TYPE <> 'TABLE'

11                    UNION

12                    SELECT T1.*

13                      FROM TMP_T1 T1, T_20170703_LHR_03 T3

14                     WHERE T1.OBJECT_ID = T3.OBJECT_ID

15                       AND T1.OBJECT_TYPE <> 'TABLE'));

COUNT(1)

----------

5060

LHR@orclasm > SELECT * FROM TABLE(DBMS_XPLAN.DISPLAY_CURSOR(NULL,NULL,'allstats last'));

PLAN_TABLE_OUTPUT

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

SQL_ID  9wy6ds1m0fmta, child number 0

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

WITH TMP_T1 AS  (SELECT T1.* FROM T_20170703_LHR_01 T1) SELECT COUNT(1)

FROM (SELECT T1.*           FROM TMP_T1 T1          WHERE

T1.OBJECT_TYPE = 'TABLE'         UNION ALL (SELECT T1.*

FROM TMP_T1 T1, T_20170703_LHR_02 T2                    WHERE

T1.OBJECT_ID = T2.OBJECT_ID                      AND T1.OBJECT_TYPE <>

'TABLE'                   UNION                   SELECT T1.*

FROM TMP_T1 T1, T_20170703_LHR_03 T3                    WHERE

T1.OBJECT_ID = T3.OBJECT_ID                      AND T1.OBJECT_TYPE <>

'TABLE'))

Plan hash value: 3651740877

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

| Id  | Operation                  | Name              | Starts | E-Rows | A-Rows |   A-Time   | Buffers |  OMem |  1Mem | Used-Mem |

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

|   0 | SELECT STATEMENT           |                   |      1 |        |      1 |00:00:00.08 |    1423 |       |       |          |

|   1 |  SORT AGGREGATE            |                   |      1 |      1 |      1 |00:00:00.08 |    1423 |       |       |          |

|   2 |   VIEW                     |                   |      1 |   4641 |   5060 |00:00:00.07 |    1423 |       |       |          |

|   3 |    UNION-ALL               |                   |      1 |        |   5060 |00:00:00.07 |    1423 |       |       |          |

|*  4 |     TABLE ACCESS FULL      | T_20170703_LHR_01 |      1 |   1631 |   3319 |00:00:00.01 |     469 |       |       |          |

|   5 |     SORT UNIQUE            |                   |      1 |   4641 |   1741 |00:00:00.07 |     954 |   178K|   178K|  158K (0)|

|   6 |      UNION-ALL             |                   |      1 |        |   2634 |00:00:00.07 |     954 |       |       |          |

|*  7 |       HASH JOIN            |                   |      1 |   2010 |   1741 |00:00:00.04 |     479 |  1452K|  1452K| 1620K (0)|

|   8 |        INDEX FAST FULL SCAN| IND_T2_OBJ_ID_1   |      1 |   2012 |   2010 |00:00:00.01 |      10 |       |       |          |

|*  9 |        TABLE ACCESS FULL   | T_20170703_LHR_01 |      1 |  76640 |  74952 |00:00:00.01 |     469 |       |       |          |

|* 10 |       HASH JOIN            |                   |      1 |   1000 |    893 |00:00:00.03 |     475 |  1452K|  1452K| 1524K (0)|

|  11 |        INDEX FAST FULL SCAN| IND_T3_OBJ_ID_1   |      1 |   1000 |   1000 |00:00:00.01 |       6 |       |       |          |

|* 12 |        TABLE ACCESS FULL   | T_20170703_LHR_01 |      1 |  76640 |  74952 |00:00:00.01 |     469 |       |       |          |

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

Predicate Information (identified by operation id):

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

4 - filter("T1"."OBJECT_TYPE"='TABLE')

7 - access("T1"."OBJECT_ID"="T2"."OBJECT_ID")

9 - filter("T1"."OBJECT_TYPE"<>'TABLE')

10 - access("T1"."OBJECT_ID"="T3"."OBJECT_ID")

12 - filter("T1"."OBJECT_TYPE"<>'TABLE')

41 rows selected.

LHR@orclasm >

LHR@orclasm > set autot on

LHR@orclasm > SELECT COUNT(1)

2    FROM T_20170703_LHR_01   T1

3   WHERE T1.OBJECT_TYPE = 'TABLE'

4      OR EXISTS (SELECT 1 FROM T_20170703_LHR_02 T2 WHERE T1.OBJECT_ID = T2.OBJECT_ID)

5      OR EXISTS (SELECT 1 FROM T_20170703_LHR_03 T3 WHERE T1.OBJECT_ID = T3.OBJECT_ID);

COUNT(1)

----------

5060

Execution Plan

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

Plan hash value: 1566256780

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

| Id  | Operation           | Name              | Rows  | Bytes | Cost (%CPU)| Time     |

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

|   0 | SELECT STATEMENT    |                   |     1 |    14 |   133   (1)| 00:00:02 |

|   1 |  SORT AGGREGATE     |                   |     1 |    14 |            |          |

|*  2 |   FILTER            |                   |       |       |            |          |

|   3 |    TABLE ACCESS FULL| T_20170703_LHR_01 | 78271 |  1070K|   133   (1)| 00:00:02 |

|*  4 |    INDEX RANGE SCAN | IND_T2_OBJ_ID_1   |     1 |     5 |     1   (0)| 00:00:01 |

|*  5 |    INDEX RANGE SCAN | IND_T3_OBJ_ID_1   |     1 |     5 |     1   (0)| 00:00:01 |

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

Predicate Information (identified by operation id):

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

2 - filter("T1"."OBJECT_TYPE"='TABLE' OR  EXISTS (SELECT 0 FROM

"T_20170703_LHR_02" "T2" WHERE "T2"."OBJECT_ID"=:B1) OR  EXISTS (SELECT 0 FROM

"T_20170703_LHR_03" "T3" WHERE "T3"."OBJECT_ID"=:B2))

4 - access("T2"."OBJECT_ID"=:B1)

5 - access("T3"."OBJECT_ID"=:B1)

Statistics

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

0  recursive calls

0  db block gets

149133  consistent gets

0  physical reads

0  redo size

527  bytes sent via SQL*Net to client

520  bytes received via SQL*Net from client

2  SQL*Net roundtrips to/from client

0  sorts (memory)

0  sorts (disk)

1  rows processed

LHR@orclasm > SELECT COUNT(1)

2    FROM (SELECT T1.*

3            FROM T_20170703_LHR_01 T1

4           WHERE T1.OBJECT_TYPE = 'TABLE'

5          UNION ALL (SELECT T1.*

6                      FROM T_20170703_LHR_01 T1, T_20170703_LHR_02 T2

7                     WHERE T1.OBJECT_ID = T2.OBJECT_ID

8                       AND T1.OBJECT_TYPE <> 'TABLE'

9                    UNION

10                    SELECT T1.*

11                      FROM T_20170703_LHR_01 T1, T_20170703_LHR_03 T3

12                     WHERE T1.OBJECT_ID = T3.OBJECT_ID

13                       AND T1.OBJECT_TYPE <> 'TABLE'));

COUNT(1)

----------

5060

Execution Plan

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

Plan hash value: 3651740877

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

| Id  | Operation                  | Name              | Rows  | Bytes | Cost (%CPU)| Time     |

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

|   0 | SELECT STATEMENT           |                   |     1 |       |   407   (2)| 00:00:05 |

|   1 |  SORT AGGREGATE            |                   |     1 |       |            |          |

|   2 |   VIEW                     |                   |  4641 |       |   407   (2)| 00:00:05 |

|   3 |    UNION-ALL               |                   |       |       |            |          |

|*  4 |     TABLE ACCESS FULL      | T_20170703_LHR_01 |  1631 | 61978 |   133   (1)| 00:00:02 |

|   5 |     SORT UNIQUE            |                   |  4641 |   186K|   407  (68)| 00:00:05 |

|   6 |      UNION-ALL             |                   |       |       |            |          |

|*  7 |       HASH JOIN            |                   |  2010 | 86430 |   137   (2)| 00:00:02 |

|   8 |        INDEX FAST FULL SCAN| IND_T2_OBJ_ID_1   |  2012 | 10060 |     3   (0)| 00:00:01 |

|*  9 |        TABLE ACCESS FULL   | T_20170703_LHR_01 | 76640 |  2844K|   133   (1)| 00:00:02 |

|* 10 |       HASH JOIN            |                   |  1000 | 43000 |   137   (2)| 00:00:02 |

|  11 |        INDEX FAST FULL SCAN| IND_T3_OBJ_ID_1   |  1000 |  5000 |     3   (0)| 00:00:01 |

|* 12 |        TABLE ACCESS FULL   | T_20170703_LHR_01 | 76640 |  2844K|   133   (1)| 00:00:02 |

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

Predicate Information (identified by operation id):

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

4 - filter("T1"."OBJECT_TYPE"='TABLE')

7 - access("T1"."OBJECT_ID"="T2"."OBJECT_ID")

9 - filter("T1"."OBJECT_TYPE"<>'TABLE')

10 - access("T1"."OBJECT_ID"="T3"."OBJECT_ID")

12 - filter("T1"."OBJECT_TYPE"<>'TABLE')

Statistics

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

0  recursive calls

0  db block gets

1423  consistent gets

0  physical reads

0  redo size

527  bytes sent via SQL*Net to client

520  bytes received via SQL*Net from client

2  SQL*Net roundtrips to/from client

1  sorts (memory)

0  sorts (disk)

1  rows processed

LHR@orclasm > WITH TMP_T1 AS

2   (SELECT T1.* FROM T_20170703_LHR_01 T1)

3  SELECT COUNT(1)

4    FROM (SELECT T1.*

5            FROM TMP_T1 T1

6           WHERE T1.OBJECT_TYPE = 'TABLE'

7          UNION ALL (SELECT T1.*

8                      FROM TMP_T1 T1, T_20170703_LHR_02 T2

9                     WHERE T1.OBJECT_ID = T2.OBJECT_ID

10                       AND T1.OBJECT_TYPE <> 'TABLE'

11                    UNION

12                    SELECT T1.*

13                      FROM TMP_T1 T1, T_20170703_LHR_03 T3

14                     WHERE T1.OBJECT_ID = T3.OBJECT_ID

15                       AND T1.OBJECT_TYPE <> 'TABLE'));

COUNT(1)

----------

5060

Execution Plan

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

Plan hash value: 3651740877

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

| Id  | Operation                  | Name              | Rows  | Bytes | Cost (%CPU)| Time     |

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

|   0 | SELECT STATEMENT           |                   |     1 |       |   407   (2)| 00:00:05 |

|   1 |  SORT AGGREGATE            |                   |     1 |       |            |          |

|   2 |   VIEW                     |                   |  4641 |       |   407   (2)| 00:00:05 |

|   3 |    UNION-ALL               |                   |       |       |            |          |

|*  4 |     TABLE ACCESS FULL      | T_20170703_LHR_01 |  1631 | 61978 |   133   (1)| 00:00:02 |

|   5 |     SORT UNIQUE            |                   |  4641 |   186K|   407  (68)| 00:00:05 |

|   6 |      UNION-ALL             |                   |       |       |            |          |

|*  7 |       HASH JOIN            |                   |  2010 | 86430 |   137   (2)| 00:00:02 |

|   8 |        INDEX FAST FULL SCAN| IND_T2_OBJ_ID_1   |  2012 | 10060 |     3   (0)| 00:00:01 |

|*  9 |        TABLE ACCESS FULL   | T_20170703_LHR_01 | 76640 |  2844K|   133   (1)| 00:00:02 |

|* 10 |       HASH JOIN            |                   |  1000 | 43000 |   137   (2)| 00:00:02 |

|  11 |        INDEX FAST FULL SCAN| IND_T3_OBJ_ID_1   |  1000 |  5000 |     3   (0)| 00:00:01 |

|* 12 |        TABLE ACCESS FULL   | T_20170703_LHR_01 | 76640 |  2844K|   133   (1)| 00:00:02 |

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

Predicate Information (identified by operation id):

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

4 - filter("T1"."OBJECT_TYPE"='TABLE')

7 - access("T1"."OBJECT_ID"="T2"."OBJECT_ID")

9 - filter("T1"."OBJECT_TYPE"<>'TABLE')

10 - access("T1"."OBJECT_ID"="T3"."OBJECT_ID")

12 - filter("T1"."OBJECT_TYPE"<>'TABLE')

Statistics

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

0  recursive calls

0  db block gets

1423  consistent gets

0  physical reads

0  redo size

527  bytes sent via SQL*Net to client

520  bytes received via SQL*Net from client

2  SQL*Net roundtrips to/from client

1  sorts (memory)

0  sorts (disk)

1  rows processed

什么是半连接、反连接和星型连接？

（一）半连接（Semi Join）

半连接（Semi Join）是一种特殊的连接类型，当做子查询展开时，Oracle经常会把那些外部WHERE条件为EXISTS、IN或= ANY的子查询转换为对应的半连接。半连接分为嵌套循环半连接（Hint为：NL_SJ）、排序合并半连接（Hint为：MERGE_SJ）和哈希半连接（Hint为：HASH_SJ），不过在新版本数据库里，都倾向于使用哈希半连接。不过哈希半连接也有一些限制条件，例如，只能使用等值连接、不能使用GROUP BY、CONNECT BY、ROWNUM等限制条件。在执行计划中若有关键字“HASH JOIN SEMI”，则说明Oracle使用了哈希半连接。示例如下所示：

SELECT * FROM  scott.DEPT A WHERE DEPTNO  IN (SELECT /*+ HASH_SJ */  DEPTNO FROM  scott.EMP);

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

| Id  | Operation          | Name | Rows  | Bytes | Cost (%CPU)| Time     |

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

|   0 | SELECT STATEMENT   |      |     3 |    69 |     7  (15)| 00:00:01 |

|*  1 |HASH JOIN SEMI|      |     3 |    69 |     7  (15)| 00:00:01 |

|   2 |   TABLE ACCESS FULL| DEPT |     4 |    80 |     3   (0)| 00:00:01 |

|   3 |   TABLE ACCESS FULL| EMP  |    14 |    42 |     3   (0)| 00:00:01 |

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

SELECT * FROM  scott.DEPT A WHERE DEPTNO  IN (SELECT /*+ MERGE_SJ */  DEPTNO FROM  scott.EMP);

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

| Id  | Operation                    | Name    | Rows  | Bytes | Cost (%CPU)| Time     |

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

|   0 | SELECT STATEMENT             |         |     3 |    69 |     6  (17)| 00:00:01 |

|   1 |MERGE JOIN SEMI|         |     3 |    69 |     6  (17)| 00:00:01 |

|   2 |   TABLE ACCESS BY INDEX ROWID| DEPT    |     4 |    80 |     2   (0)| 00:00:01 |

|   3 |    INDEX FULL SCAN           | PK_DEPT |     4 |       |     1   (0)| 00:00:01 |

|*  4 |   SORT UNIQUE                |         |    14 |    42 |     4  (25)| 00:00:01 |

|   5 |    TABLE ACCESS FULL         | EMP     |    14 |    42 |     3   (0)| 00:00:01 |

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

SELECT * FROM  scott.DEPT A WHERE DEPTNO  IN (SELECT /*+ NL_SJ */  DEPTNO FROM  scott.EMP);

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

| Id  | Operation          | Name | Rows  | Bytes | Cost (%CPU)| Time     |

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

|   0 | SELECT STATEMENT   |      |     3 |    69 |    10   (0)| 00:00:01 |

|   1 |NESTED LOOPS SEMI|      |     3 |    69 |    10   (0)| 00:00:01 |

|   2 |   TABLE ACCESS FULL| DEPT |     4 |    80 |     3   (0)| 00:00:01 |

|*  3 |   TABLE ACCESS FULL| EMP  |     9 |    27 |     2   (0)| 00:00:01 |

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

（二）反连接（Anti Join）

反连接（Anti Join）也是一种特殊的连接类型，通常用于从一个表中返回不在另一个数据源中的数据行。当做子查询展开时，Oracle经常会把那些外部WHERE条件为NOT EXISTS、NOT IN或<> ALL的子查询转换成对应的反连接。反连接分为嵌套循环反连接（NESTED LOOPS ANTI，Hint为：NL_AJ）、排序合并反连接（MERGE JOIN ANTI，Hint为：MERGE_AJ）和哈希反连接（HASH JOIN ANTI，Hint为：HASH_AJ）。示例如下所示：

CREATE TABLE EMP AS SELECT * FROM SCOTT.EMP;

CREATE TABLE DEPT AS SELECT * FROM SCOTT.DEPT;

SELECT * FROM EMP A WHERE NOT EXISTS(SELECT 1 FROM DEPT WHERE DEPTNO=A.DEPTNO);

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

| Id  | Operation          | Name | Rows  | Bytes | Cost (%CPU)| Time     |

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

|   0 | SELECT STATEMENT   |      |     2 |    84 |     5  (20)| 00:00:01 |

|*  1 |HASH JOIN ANTI|      |     2 |    84 |     5  (20)| 00:00:01 |

|   2 |   TABLE ACCESS FULL| EMP  |    12 |   468 |     2   (0)| 00:00:01 |

|   3 |   TABLE ACCESS FULL| DEPT |     4 |    12 |     2   (0)| 00:00:01 |

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

SELECT * FROM EMP A WHERE NOT EXISTS(SELECT /*+NL_AJ*/ 1 FROM DEPT WHERE DEPTNO=A.DEPTNO);

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

| Id  | Operation          | Name | Rows  | Bytes | Cost (%CPU)| Time     |

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

|   0 | SELECT STATEMENT   |      |     2 |    84 |     7   (0)| 00:00:01 |

|   1 |NESTED LOOPS ANTI|      |     2 |    84 |     7   (0)| 00:00:01 |

|   2 |   TABLE ACCESS FULL| EMP  |    12 |   468 |     2   (0)| 00:00:01 |

|*  3 |   TABLE ACCESS FULL| DEPT |     4 |    12 |     0   (0)| 00:00:01 |

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

SELECT * FROM EMP A WHERE NOT EXISTS(SELECT /*+MERGE_AJ*/ 1 FROM DEPT WHERE DEPTNO=A.DEPTNO);

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

| Id  | Operation           | Name | Rows  | Bytes | Cost (%CPU)| Time     |

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

|   0 | SELECT STATEMENT    |      |     2 |    84 |     6  (34)| 00:00:01 |

|   1 |MERGE JOIN ANTI|      |     2 |    84 |     6  (34)| 00:00:01 |

|   2 |   SORT JOIN         |      |    12 |   468 |     3  (34)| 00:00:01 |

|   3 |    TABLE ACCESS FULL| EMP  |    12 |   468 |     2   (0)| 00:00:01 |

|*  4 |   SORT UNIQUE       |      |     4 |    12 |     3  (34)| 00:00:01 |

|   5 |    TABLE ACCESS FULL| DEPT |     4 |    12 |     2   (0)| 00:00:01 |

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

需要注意的是，NOT IN和<> ALL对NULL值敏感，这意味着NOT IN后面的子查询或者常量集合一旦有NULL值出现，则整个SQL的执行结果就会为NULL，即此时的执行结果将不包含任何记录。但是，NOT EXISTS对NULL值不敏感，这意味着NULL值对NOT EXISTS的执行结果不会有什么影响。正是因为NOT IN和<> ALL对NULL值敏感，所以一旦相关的连接列上出现了NULL值，此时Oracle如果还按照通常的反连接的处理逻辑来处理，得到的结果就不对了。为了解决NOT IN和<> ALL对NULL值敏感的问题，Oracle推出了改良的反连接，这种反连接能够处理NULL值，Oracle称其为Null-Aware Anti Join，如下例：

SELECT * FROM DEPT A WHERE DEPTNO NOT IN (SELECT DEPTNO FROM EMP);

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

| Id  | Operation          | Name | Rows  | Bytes | Cost (%CPU)| Time     |

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

|   0 | SELECT STATEMENT   |      |     1 |    23 |     5  (20)| 00:00:01 |

|*  1 |HASH JOIN ANTI NA|      |     1 |    23 |     5  (20)| 00:00:01 |

|   2 |   TABLE ACCESS FULL| DEPT |     4 |    80 |     2   (0)| 00:00:01 |

|   3 |   TABLE ACCESS FULL| EMP  |    12 |    36 |     2   (0)| 00:00:01 |

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

执行步骤的列Operation的值为“HASH JOIN ANTI NA”，关键字“NA”就是Null-Aware的缩写，表示这里采用的不是普通的哈希反连接，而是改良后的、能够处理NULL值的哈希反连接。

在Oracle 11gR2中，Oracle是否启用Null-Aware Anti Join受隐含参数“_OPTIMIZER_NULL_AWARE_ANTIJOIN”控制，其默认值为TRUE，表示启用Null-Aware Anti Join。如果把该参数的值修改为FALSE，那么表示Oracle就不能再用Null-Aware Anti Join了，而又因为NOT IN对NULL值敏感，所以Oracle此时也不能用普通的反连接。关于该隐含参数的查询如下所示：

SYS@orclasm > set pagesize 9999

SYS@orclasm > set line 9999

SYS@orclasm > col NAME format a40

SYS@orclasm > col KSPPDESC format a50

SYS@orclasm > col KSPPSTVL format a20

SYS@orclasm > SELECT a.INDX,

2         a.KSPPINM NAME,

3         a.KSPPDESC,

4         b.KSPPSTVL

5  FROM   x$ksppi  a,

6         x$ksppcv b

7  WHERE  a.INDX = b.INDX

8  and lower(a.KSPPINM) like  lower('%?meter%');

Enter value for parameter: _OPTIMIZER_NULL_AWARE_ANTIJOIN

old   8: and lower(a.KSPPINM) like  lower('%?meter%')

new   8: and lower(a.KSPPINM) like  lower('%_OPTIMIZER_NULL_AWARE_ANTIJOIN%')

INDX NAME                                     KSPPDESC                                           KSPPSTVL

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

1907 _optimizer_null_aware_antijoin           null-aware antijoin parameter                      TRUE

filter这个操作在《Cost Based Oracle Fundamental》此书第九章有介绍。filter的操作是对外表的每一行，都要对内表执行一次全表扫描，所以很多时候提到filter都会感到可怕。他其实很像我们熟悉的neested loop，但它的独特之处在于会维护一个hash table。其实filter 的性能实际上跟列值distinct数有关，oracle在执行的时候实际上做了很大优化，最坏情况下才会出现对外表每一行执行一次filter操作，如果distinct值比较少，那执行效率还是非常高的。甚至有可能比nl更高。

针对filter用一个简单的实例来解释一下：

假如表TMP_LIUHC_1和TMP_LIUHC_2，如果执行如下语句：

如果TMP_LIUHC_1里取出object_id=1，那么对于TMP_LIUHC_2来说即select 1 from TMP_LIUHC_2 where TMP_LIUHC_2.object_id*10=1,如果条件满足，那么对于子查询，输入输出对，即为(1（TMP_LIUHC_1.object_id）,1（常量）)。他存储在hash table里，并且由于条件满足，TMP_LIUHC_1.object_id=1被放入结果集。然后接着从TMP_LIUHC_1取出object_id=2，如果子查询依旧条件满足，那么子查询产生另一个输入和输出，即(2,1)，被放入hash table里；并且TMP_LIUHC_1.object_id=2被放入结果集。接着假设TMP_LIUHC_1里有重复的object_id，例如我们第三次从TMP_LIUHC_1取出的object_id=2,那么由于我们对于子查询来说，已经有输入输出对(2,1)在hash table里了，所以就不用去再次全表扫描TMP_LIUHC_2了，ORACLE非常聪明地知道object_id=2是结果集。这里，filter和neested loop相比,省去了一次全表扫描TMP_LIUHC_2。这个hash table是有大小限制的，当被占满的时候，后续新的TMP_LIUHC_1.object_id的FILTER就类似neested loop了。由此可见，从buffer gets层面上来看，FILTER是应该优于neested loop的，尤其当外部查询需要传递给子查询的输入（此例中为TMP_LIUHC_1.object_id）的distinct value非常小时，FILTER就会显得更优。即使在我这个例子中，TMP_LIUHC_1.object_id的distinct value上万，我对比了一下neested loop，FILTER仍然略优：
查看关联列的distinct值
SQL> select count(distinct object_type) from TMP_LIUHC_1;
COUNT(DISTINCTOBJECT_TYPE)
--------------------------
40
SQL> select count(distinct object_id) from TMP_LIUHC_1;
COUNT(DISTINCTOBJECT_ID)
------------------------
60947
下面使用filter
下面使用嵌套(NL)
完全跑不出来。。。。
由此可见，当外围输入值(就是关联值)的distinct的值很少时，使用filter大大的提高查询效率。

About Me

...............................................................................................................................

● 本文作者：小麦苗，只专注于数据库的技术，更注重技术的运用

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