在Oracle中，举例说明“连接因式分解（Join factorization，JF）”查询转换。
♣ 答案部分
1LHR@orclasm > SELECT /*+FULL(A) FULL(B)*/ A.*,B.DNAME FROM SCOTT.EMP A,SCOTT.DEPT B WHERE A.DEPTNO=B.DEPTNO AND A.EMPNO=6
2 2 UNION ALL
3 3 SELECT /*+FULL(A) FULL(B)*/ A.*,B.DNAME FROM SCOTT.EMP A,SCOTT.DEPT B WHERE A.DEPTNO=B.DEPTNO AND A.EMPNO=7;
4
5no rows selected
6
7
8Execution Plan
9----------------------------------------------------------
10Plan hash value: 1245103347
11
12-------------------------------------------------------------------------------------------
13| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
14-------------------------------------------------------------------------------------------
15| 0 | SELECT STATEMENT | | 2 | 244 | 8 (13)| 00:00:01 |
16|* 1 | HASH JOIN | | 2 | 244 | 8 (13)| 00:00:01 |
17| 2 | VIEW | VW_JF_SET$623BBB07 | 2 | 200 | 4 (0)| 00:00:01 |
18| 3 | UNION-ALL | | | | | |
19|* 4 | TABLE ACCESS FULL| EMP | 1 | 87 | 2 (0)| 00:00:01 |
20|* 5 | TABLE ACCESS FULL| EMP | 1 | 87 | 2 (0)| 00:00:01 |
21| 6 | TABLE ACCESS FULL | DEPT | 4 | 88 | 3 (0)| 00:00:01 |
22-------------------------------------------------------------------------------------------
23
24Predicate Information (identified by operation id):
25---------------------------------------------------
26
27 1 - access("ITEM_1"="B"."DEPTNO")
28 4 - filter("A"."EMPNO"=6)
29 5 - filter("A"."EMPNO"=7)
30
31Note
32-----
33 - dynamic sampling used for this statement (level=2)
34
35
36Statistics
37----------------------------------------------------------
38 99 recursive calls
39 7 db block gets
40 32 consistent gets
41 0 physical reads
42 4536 redo size
43 866 bytes sent via SQL*Net to client
44 509 bytes received via SQL*Net from client
45 1 SQL*Net roundtrips to/from client
46 0 sorts (memory)
47 0 sorts (disk)
48 0 rows processed
49
50LHR@orclasm > ALTER SESSION SET "_OPTIMIZER_JOIN_FACTORIZATION"=FALSE;
51
52Session altered.
53
54LHR@orclasm > SELECT /*+FULL(A) FULL(B)*/ A.*,B.DNAME FROM SCOTT.EMP A,SCOTT.DEPT B WHERE A.DEPTNO=B.DEPTNO AND A.EMPNO=6
55 2 UNION ALL
56 3 SELECT /*+FULL(A) FULL(B)*/ A.*,B.DNAME FROM SCOTT.EMP A,SCOTT.DEPT B WHERE A.DEPTNO=B.DEPTNO AND A.EMPNO=7;
57
58no rows selected
59
60
61Execution Plan
62----------------------------------------------------------
63Plan hash value: 2703228680
64
65----------------------------------------------------------------------------
66| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
67----------------------------------------------------------------------------
68| 0 | SELECT STATEMENT | | 2 | 218 | 8 (50)| 00:00:01 |
69| 1 | UNION-ALL | | | | | |
70| 2 | NESTED LOOPS | | 1 | 109 | 4 (0)| 00:00:01 |
71|* 3 | TABLE ACCESS FULL| EMP | 1 | 87 | 2 (0)| 00:00:01 |
72|* 4 | TABLE ACCESS FULL| DEPT | 82 | 1804 | 2 (0)| 00:00:01 |
73| 5 | NESTED LOOPS | | 1 | 109 | 4 (0)| 00:00:01 |
74|* 6 | TABLE ACCESS FULL| EMP | 1 | 87 | 2 (0)| 00:00:01 |
75|* 7 | TABLE ACCESS FULL| DEPT | 82 | 1804 | 2 (0)| 00:00:01 |
76----------------------------------------------------------------------------
77
78Predicate Information (identified by operation id):
79---------------------------------------------------
80
81 3 - filter("A"."EMPNO"=6)
82 4 - filter("A"."DEPTNO"="B"."DEPTNO")
83 6 - filter("A"."EMPNO"=7)
84 7 - filter("A"."DEPTNO"="B"."DEPTNO")
85
86
87Statistics
88----------------------------------------------------------
89 93 recursive calls
90 7 db block gets
91 14 consistent gets
92 0 physical reads
93 4536 redo size
94 866 bytes sent via SQL*Net to client
95 509 bytes received via SQL*Net from client
96 1 SQL*Net roundtrips to/from client
97 0 sorts (memory)
98 0 sorts (disk)
99 0 rows processed
本文选自《Oracle程序员面试笔试宝典》，作者：李华荣。
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