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题目部分
在Oracle中，举例说明“集合操作关联转变（Set Join Conversion）”查询转换。
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答案部分
1LHR@orclasm > SELECT * FROM SCOTT.EMP A WHERE A.EMPNO>7469
2 2 MINUS
3 3 SELECT * FROM SCOTT.EMP A WHERE A.EMPNO>7839;
4
5Execution Plan
6----------------------------------------------------------
7Plan hash value: 3686975449
8
9----------------------------------------------------------------------------
10| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
11----------------------------------------------------------------------------
12| 0 | SELECT STATEMENT | | 13 | 1566 | 8 (63)| 00:00:01 |
13| 1 | MINUS | | | | | |
14| 2 | SORT UNIQUE | | 13 | 1131 | 4 (25)| 00:00:01 |
15|* 3 | TABLE ACCESS FULL| EMP | 13 | 1131 | 3 (0)| 00:00:01 |
16| 4 | SORT UNIQUE | | 5 | 435 | 4 (25)| 00:00:01 |
17|* 5 | TABLE ACCESS FULL| EMP | 5 | 435 | 3 (0)| 00:00:01 |
18----------------------------------------------------------------------------
19
20Predicate Information (identified by operation id):
21---------------------------------------------------
22
23 3 - filter("A"."EMPNO">7469)
24 5 - filter("A"."EMPNO">7839)
25
26Note
27-----
28 - dynamic sampling used for this statement (level=2)
29
30
31Statistics
32----------------------------------------------------------
33 61 recursive calls
34 5 db block gets
35 34 consistent gets
36 0 physical reads
37 2536 redo size
38 1357 bytes sent via SQL*Net to client
39 520 bytes received via SQL*Net from client
40 2 SQL*Net roundtrips to/from client
41 2 sorts (memory)
42 0 sorts (disk)
43 8 rows processed
44
45LHR@orclasm >
46LHR@orclasm > ALTER SESSION SET "_CONVERT_SET_TO_JOIN"=TRUE;
47
48Session altered.
49
50LHR@orclasm >
51LHR@orclasm > SELECT * FROM SCOTT.EMP A WHERE A.EMPNO>7469
52 2 MINUS
53 3 SELECT * FROM SCOTT.EMP A WHERE A.EMPNO>7839;
54
55Execution Plan
56----------------------------------------------------------
57Plan hash value: 3353202012
58
59---------------------------------------------------------------------------
60| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
61---------------------------------------------------------------------------
62| 0 | SELECT STATEMENT | | 13 | 2262 | 7 (15)| 00:00:01 |
63|* 1 | HASH JOIN ANTI | | 13 | 2262 | 7 (15)| 00:00:01 |
64|* 2 | TABLE ACCESS FULL| EMP | 13 | 1131 | 3 (0)| 00:00:01 |
65|* 3 | TABLE ACCESS FULL| EMP | 5 | 435 | 3 (0)| 00:00:01 |
66---------------------------------------------------------------------------
67
68Predicate Information (identified by operation id):
69---------------------------------------------------
70
71 1 - access("A"."EMPNO"="A"."EMPNO" AND
72 SYS_OP_MAP_NONNULL("A"."ENAME")=SYS_OP_MAP_NONNULL("A"."ENAME") AND
73 SYS_OP_MAP_NONNULL("A"."JOB")=SYS_OP_MAP_NONNULL("A"."JOB") AND
74 SYS_OP_MAP_NONNULL("A"."MGR")=SYS_OP_MAP_NONNULL("A"."MGR") AND
75 SYS_OP_MAP_NONNULL("A"."HIREDATE")=SYS_OP_MAP_NONNULL("A"."HIREDATE")
76 AND SYS_OP_MAP_NONNULL("A"."SAL")=SYS_OP_MAP_NONNULL("A"."SAL") AND
77 SYS_OP_MAP_NONNULL("A"."COMM")=SYS_OP_MAP_NONNULL("A"."COMM") AND
78 SYS_OP_MAP_NONNULL("A"."DEPTNO")=SYS_OP_MAP_NONNULL("A"."DEPTNO"))
79 2 - filter("A"."EMPNO">7469)
80 3 - filter("A"."EMPNO">7839)
81
82Note
83-----
84 - dynamic sampling used for this statement (level=2)
85
86
87Statistics
88----------------------------------------------------------
89 61 recursive calls
90 5 db block gets
91 34 consistent gets
92 0 physical reads
93 2552 redo size
94 1347 bytes sent via SQL*Net to client
95 520 bytes received via SQL*Net from client
96 2 SQL*Net roundtrips to/from client
97 0 sorts (memory)
98 0 sorts (disk)
99 8 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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