Oracle 利用执行计划来避免排序操作

在oracle中，利用index来避免排序

SQL> CREATE TABLE T_NOSORT (ID NUMBER PRIMARY KEY, NAME VARCHAR2(30) NOT NULL);

SQL> CREATE INDEX IND_T_NOSORT_NAME ON T_NOSORT(NAME);

SQL> INSERT INTO T_NOSORT SELECT ROWNUM, TABLE_NAME FROM USER_TABLES;

SQL> COMMIT;

SQL> SET AUTOT ON EXP

SQL> SELECT ID, NAME FROM T_NOSORT ORDER BY NAME;

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

Plan hash value: 1041838668

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

| Id | Operation | Name | Rows | Bytes |

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

| 0 | SELECT STATEMENT | | 15 | 450 |

| 1 | SORT ORDER BY | | 15 | 450 |

| 2 | TABLE ACCESS FULL| T_NOSORT | 15 | 450 |

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

QL> SELECT /*+ INDEX(T_NOSORT IND_T_NOSORT_NAME) */ ID, NAME FROM T_NOSORT ORDER BY NAME;

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

-------------------------------------------------------------------------------|   0 | SELECT STATEMENT          |                   |    41 |  1230 |   827   (1)| 00:00:10 |

|   1 |  TABLE ACCESS BY INDEX ROWID| T_NOSORT          |    41 |  1230 |   827   (1)| 00:00:10 |

|   2 |   INDEX FULL SCAN           | IND_T_NOSORT_NAME |    41 |       |    26   (0)| 00:00:01 |

利用索引范围扫描

SQL> SELECT ID, NAME FROM T_NOSORT WHERE NAME < 'I' ORDER BY NAME;

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

Plan hash value: 1041838668

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

| Id | Operation | Name | Rows | Bytes |

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

| 0 | SELECT STATEMENT | | 9 | 270 |

| 1 | SORT ORDER BY | | 9 | 270 |

|* 2 | TABLE ACCESS FULL| T_NOSORT | 9 | 270 |

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

Predicate Information (identified by operation id):

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

2 - filter("NAME"<'I')

SQL> SELECT /*+ INDEX(T_NOSORT IND_T_NOSORT_NAME) */ ID, NAME 

2 FROM T_NOSORT WHERE NAME < 'I' ORDER BY NAME;

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

Plan hash value: 919790285

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

| Id | Operation | Name | Rows | Bytes |

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

| 0 | SELECT STATEMENT | | 9 | 270 |

| 1 | TABLE ACCESS BY INDEX ROWID| T_NOSORT | 9 | 270 |

|* 2 | INDEX RANGE SCAN | IND_T_NOSORT_NAME | 9 | |

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

Predicate Information (identified by operation id):

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

2 - access("NAME"<'I')

filter("NAME"<'I')

如果是倒序排序

QL> SELECT /*+ INDEX_DESC(T_NOSORT IND_T_NOSORT_NAME) */ ID, NAME 

2 FROM T_NOSORT ORDER BY NAME DESC;

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

Plan hash value: 2858378269

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

| Id | Operation | Name | Rows | Bytes |

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

| 0 | SELECT STATEMENT | | 15 | 450 |

| 1 | TABLE ACCESS BY INDEX ROWID| T_NOSORT | 15 | 450 |

| 2 | INDEX FULL SCAN DESCENDING| IND_T_NOSORT_NAME | 15 | |

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

这里只是说明了能够避免排序的执行计划，但是不一定能提升性能

上面针对于单表

MERGE JOIN连接方式

SQL> CREATE TABLE T1 (ID NUMBER PRIMARY KEY, NAME VARCHAR2(30) NOT NULL);

SQL> CREATE TABLE T2 (ID NUMBER, NAME VARCHAR2(30));

SQL> CREATE INDEX IND_T1_NAME ON T1(NAME);

SQL> INSERT INTO T1 SELECT ROWNUM, TABLE_NAME FROM USER_TABLES;

SQL> INSERT INTO T2 SELECT ROWNUM, OBJECT_NAME FROM USER_OBJECTS;

SQL> COMMIT;

SQL> SET AUTOT ON EXP

SQL> SELECT /*+ USE_MERGE(T1, T2) */ T2.NAME, T1.ID FROM T1, T2

 WHERE T1.NAME = T2.NAME ;

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

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

|   0 | SELECT STATEMENT    |      |    41 |  1927 |     8  (25)| 00:00:01 |

|   1 |  MERGE JOIN         |      |    41 |  1927 |     8  (25)| 00:00:01 |

|   2 |   SORT JOIN         |      |    41 |  1230 |     4  (25)| 00:00:01 |

|   3 |    TABLE ACCESS FULL| T1   |    41 |  1230 |     3   (0)| 00:00:01 |

|*  4 |   SORT JOIN         |      |    99 |  1683 |     4  (25)| 00:00:01 |

|   5 |    TABLE ACCESS FULL| T2   |    99 |  1683 |     3   (0)| 00:00:01 |

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

Predicate Information (identified by operation id):

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

4 - access("T1"."NAME"="T2"."NAME")

filter("T1"."NAME"="T2"."NAME")

SQL> SELECT /*+ USE_MERGE(T2, T1) */ T2.NAME, T1.ID

 FROM T1, T2 WHERE T1.NAME = T2.NAME ORDER BY T2.NAME ;

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

Plan hash value: 412793182

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

| Id | Operation | Name | Rows | Bytes |

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

| 0 | SELECT STATEMENT | | 19 | 893 |

| 1 | MERGE JOIN | | 19 | 893 |

| 2 | SORT JOIN | | 17 | 510 |

| 3 | TABLE ACCESS FULL| T1 | 17 | 510 |

|* 4 | SORT JOIN | | 97 | 1649 |

| 5 | TABLE ACCESS FULL| T2 | 97 | 1649 |

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

Predicate Information (identified by operation id):

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

4 - access("T1"."NAME"="T2"."NAME")

filter("T1"."NAME"="T2"."NAME")

针对merge join只能对连接的列排序，且排序操作只能是升序

SQL> SELECT /*+ USE_MERGE(T2, T1) */ T2.NAME, T1.ID

 FROM T1, T2 WHERE T1.NAME = T2.NAME ORDER BY T2.NAME DESC;

|   0 | SELECT STATEMENT     |      |    41 |  1927 |     9  (34)| 00:00:01 |

|   1 |  SORT ORDER BY       |      |    41 |  1927 |     9  (34)| 00:00:01 |

|   2 |   MERGE JOIN         |      |    41 |  1927 |     8  (25)| 00:00:01 |

|   3 |    SORT JOIN         |      |    41 |  1230 |     4  (25)| 00:00:01 |

|   4 |     TABLE ACCESS FULL| T1   |    41 |  1230 |     3   (0)| 00:00:01 |

|*  5 |    SORT JOIN         |      |    99 |  1683 |     4  (25)| 00:00:01 |

|   6 |     TABLE ACCESS FULL| T2   |    99 |  1683 |     3   (0)| 00:00:01 |5 - access("T1"."NAME"="T2"."NAME")

filter("T1"."NAME"="T2"."NAME")

NESTED LOOP连接

由于nested loop不会对操作结果排序，所以结果是无序的

如果驱动表在连接前是有序的，在连接后，结果还是有序的

SQL> CREATE INDEX IND_T2_ID ON T2(ID);

SQL> CREATE INDEX IND_T2_NAME ON T2(NAME);

SQL> SELECT /*+ USE_NL(T1, T2) */ T1.ID, T1.NAME, T2.NAME 

2 FROM T1, T2

3 WHERE T1.ID = T2.ID

4 ;

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

Plan hash value: 3621112097

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

| Id | Operation | Name | Rows | Bytes | Cost

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

| 0 | SELECT STATEMENT | | 17 | 1020 | 

| 1 | TABLE ACCESS BY INDEX ROWID| T2 | 1 | 30 | 

| 2 | NESTED LOOPS | | 17 | 1020 | 

| 3 | TABLE ACCESS FULL | T1 | 17 | 510 | 

|* 4 | INDEX RANGE SCAN | IND_T2_ID | 1 | | 

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

Predicate Information (identified by operation id):

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

4 - access("T1"."ID"="T2"."ID")

SQL> SELECT /*+ ORDERED INDEX(T1 IND_T1_NAME) USE_NL(T1, T2) */ 

2 T1.ID, T1.NAME, T2.NAME 

3 FROM T1, T2

4 WHERE T1.ID = T2.ID

5 ORDER BY T1.NAME

6 ;

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

Plan hash value: 1062594094

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

| Id | Operation | Name | Rows | Bytes |

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

| 0 | SELECT STATEMENT | | 17 | 1020 |

| 1 | TABLE ACCESS BY INDEX ROWID | T2 | 1 | 30 |

| 2 | NESTED LOOPS | | 17 | 1020 |

| 3 | TABLE ACCESS BY INDEX ROWID| T1 | 17 | 510 |

| 4 | INDEX FULL SCAN | IND_T1_NAME | 17 | |

|* 5 | INDEX RANGE SCAN | IND_T2_ID | 1 | |

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

Predicate Information (identified by operation id):

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

5 - access("T1"."ID"="T2"."ID")

SQL> ALTER TABLE T2 MODIFY NAME NOT NULL;

SQL> CREATE INDEX IND_T2_NAME ON T2(NAME);

SQL> SET AUTOT OFF

SQL> UPDATE T2 SET ID = MOD(ID, 17) + 1;

SQL> COMMIT;

SQL> SET AUTOT ON EXP

SQL> SELECT /*+ ORDERED INDEX(T1 IND_T1_NAME) 

2 INDEX(T2 IND_T2_NAME) USE_NL(T1, T2) */ 

3 T1.ID, T1.NAME, T2.NAME 

4 FROM T1, T2

5 WHERE T1.ID = T2.ID

6 ORDER BY T1.NAME

7 ;

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

Plan hash value: 3719138605

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

| Id | Operation | Name | Rows | Bytes |

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

| 0 | SELECT STATEMENT | | 97 | 5820 |

|* 1 | TABLE ACCESS BY INDEX ROWID | T2 | 6 | 180 |

| 2 | NESTED LOOPS | | 97 | 5820 |

| 3 | TABLE ACCESS BY INDEX ROWID| T1 | 17 | 510 |

| 4 | INDEX FULL SCAN | IND_T1_NAME | 17 | |

| 5 | INDEX FULL SCAN | IND_T2_NAME | 97 | |

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

Predicate Information (identified by operation id):

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

1 - filter("T1"."ID"="T2"."ID")

SQL> SELECT /*+ ORDERED INDEX(T1 IND_T1_NAME) 

2 INDEX_DESC(T2 IND_T2_NAME) USE_NL(T1, T2) */ 

3 T1.ID, T1.NAME, T2.NAME 

4 FROM T1, T2

5 WHERE T1.ID = T2.ID

6 ORDER BY T1.NAME

7 ;

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

Plan hash value: 2531946081

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

| Id | Operation | Name | Rows | Bytes |

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

| 0 | SELECT STATEMENT | | 97 | 5820 |

|* 1 | TABLE ACCESS BY INDEX ROWID | T2 | 6 | 180 |

| 2 | NESTED LOOPS | | 97 | 5820 |

| 3 | TABLE ACCESS BY INDEX ROWID| T1 | 17 | 510 |

| 4 | INDEX FULL SCAN | IND_T1_NAME | 17 | |

| 5 | INDEX FULL SCAN DESCENDING | IND_T2_NAME | 97 | |

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

Predicate Information (identified by operation id):

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

1 - filter("T1"."ID"="T2"."ID")

SQL> SELECT /*+ ORDERED INDEX(T1 IND_T1_NAME) 

2 INDEX(T2 IND_T2_NAME) USE_NL(T1, T2) */ 

3 T1.ID, T1.NAME, T2.NAME 

4 FROM T1, T2

5 WHERE T1.ID = T2.ID

6 ORDER BY T1.NAME, T2.NAME DESC

7 ;

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

Plan hash value: 1438746903

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

| Id | Operation | Name | Rows | Bytes |

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

| 0 | SELECT STATEMENT | | 97 | 5820 |

| 1 | SORT ORDER BY | | 97 | 5820 |

|* 2 | TABLE ACCESS BY INDEX ROWID | T2 | 6 | 180 |

| 3 | NESTED LOOPS | | 97 | 5820 |

| 4 | TABLE ACCESS BY INDEX ROWID| T1 | 17 | 510 |

| 5 | INDEX FULL SCAN | IND_T1_NAME | 17 | |

| 6 | INDEX FULL SCAN | IND_T2_NAME | 97 | |

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

Predicate Information (identified by operation id):

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

2 - filter("T1"."ID"="T2"."ID")

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Oracle 利用执行计划来避免排序操作

MERGE JOIN连接方式

NESTED LOOP连接

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