♣ 题目 部分
在Oracle中，和视图相关的查询转换有哪些？
♣ 答案部分
（一）简单视图合并
1CREATE OR REPLACE VIEW VW_SVM_LHR AS SELECT * FROM SCOTT.EMP WHERE EMPNO<>7369;
2SELECT * FROM VW_SVM_LHR V WHERE V.JOB='DBA';
3Execution Plan
4----------------------------------------------------------
5Plan hash value: 3956160932
6
7--------------------------------------------------------------------------
8| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
9--------------------------------------------------------------------------
10| 0 | SELECT STATEMENT | | 3 | 114 | 3 (0)| 00:00:01 |
11|* 1 | TABLE ACCESS FULL| EMP | 3 | 114 | 3 (0)| 00:00:01 |
12--------------------------------------------------------------------------
13
14Predicate Information (identified by operation id):
15---------------------------------------------------
16
17 1 - filter("JOB"='DBA' AND "EMPNO"<>7369)
18
19
20
21LHR@orclasm > SELECT /*+ NO_MERGE(V)*/ * FROM VW_SVM_LHR V WHERE V.JOB='DBA';
22
23no rows selected
24
25
26Execution Plan
27----------------------------------------------------------
28Plan hash value: 45352968
29
30---------------------------------------------------------------------------------
31| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
32---------------------------------------------------------------------------------
33| 0 | SELECT STATEMENT | | 3 | 261 | 3 (0)| 00:00:01 |
34| 1 | VIEW | VW_SVM_LHR | 3 | 261 | 3 (0)| 00:00:01 |
35|* 2 | TABLE ACCESS FULL| EMP | 3 | 114 | 3 (0)| 00:00:01 |
36---------------------------------------------------------------------------------
37
38Predicate Information (identified by operation id):
39---------------------------------------------------
40
41 2 - filter("JOB"='DBA' AND "EMPNO"<>7369)
42
43LHR@orclasm > ALTER SESSION SET "_SIMPLE_VIEW_MERGING"=FALSE;
44
45Session altered.
46
47LHR@orclasm > SELECT * FROM VW_SVM_LHR V WHERE V.JOB='DBA';
48
49no rows selected
50
51
52Execution Plan
53----------------------------------------------------------
54Plan hash value: 45352968
55
56---------------------------------------------------------------------------------
57| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
58---------------------------------------------------------------------------------
59| 0 | SELECT STATEMENT | | 3 | 261 | 3 (0)| 00:00:01 |
60| 1 | VIEW | VW_SVM_LHR | 3 | 261 | 3 (0)| 00:00:01 |
61|* 2 | TABLE ACCESS FULL| EMP | 3 | 114 | 3 (0)| 00:00:01 |
62---------------------------------------------------------------------------------
63
64Predicate Information (identified by operation id):
65---------------------------------------------------
66
67 2 - filter("JOB"='DBA' AND "EMPNO"<>7369)
（二）外连接视图合并（Outer Join View Merging）
1CREATE OR REPLACE VIEW VW_SVM_LHR AS SELECT * FROM SCOTT.EMP WHERE EMPNO<>7369;
2SELECT * FROM VW_SVM_LHR V,SCOTT.DEPT T WHERE V.DEPTNO=T.DEPTNO(+);
3---------------------------------------------------------------------------
4| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
5---------------------------------------------------------------------------
6| 0 | SELECT STATEMENT | | 13 | 754 | 7 (15)| 00:00:01 |
7|* 1 | HASH JOIN OUTER | | 13 | 754 | 7 (15)| 00:00:01 |
8|* 2 | TABLE ACCESS FULL| EMP | 13 | 494 | 3 (0)| 00:00:01 |
9| 3 | TABLE ACCESS FULL| DEPT | 4 | 80 | 3 (0)| 00:00:01 |
10---------------------------------------------------------------------------
11
12Predicate Information (identified by operation id):
13---------------------------------------------------
14
15 1 - access("DEPTNO"="T"."DEPTNO"(+))
16 2 - filter("EMPNO"<>7369)
17
18
19--视图作为被驱动表：
20SELECT /*+ FULL(T)*/ * FROM VW_SVM_LHR V,SCOTT.DEPT T WHERE V.DEPTNO(+)=T.DEPTNO;
21---------------------------------------------------------------------------
22| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
23---------------------------------------------------------------------------
24| 0 | SELECT STATEMENT | | 13 | 754 | 7 (15)| 00:00:01 |
25|* 1 | HASH JOIN OUTER | | 13 | 754 | 7 (15)| 00:00:01 |
26| 2 | TABLE ACCESS FULL| DEPT | 4 | 80 | 3 (0)| 00:00:01 |
27|* 3 | TABLE ACCESS FULL| EMP | 13 | 494 | 3 (0)| 00:00:01 |
28---------------------------------------------------------------------------
29Predicate Information (identified by operation id):
30---------------------------------------------------
31
32 1 - access("DEPTNO"(+)="T"."DEPTNO")
33 3 - filter("EMPNO"(+)<>7369)
34
35
36--视图含有2个表：
37CREATE OR REPLACE VIEW VW_SVM2_LHR AS SELECT /*+ FULL(A) FULL(B)*/ A.*,B.DNAME FROM SCOTT.EMP A,SCOTT.DEPT B WHERE A.DEPTNO=B.DEPTNO AND EMPNO<>7369;
38SELECT /*+ FULL(T)*/ * FROM VW_SVM2_LHR V,SCOTT.DEPT T WHERE V.DEPTNO(+)=T.DEPTNO;
39------------------------------------------------------------------------------------
40| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
41------------------------------------------------------------------------------------
42| 0 | SELECT STATEMENT | | 13 | 1508 | 10 (10)| 00:00:01 |
43|* 1 | HASH JOIN OUTER | | 13 | 1508 | 10 (10)| 00:00:01 |
44| 2 | TABLE ACCESS FULL | DEPT | 4 | 80 | 3 (0)| 00:00:01 |
45| 3 | VIEW | VW_SVM2_LHR | 13 | 1248 | 7 (15)| 00:00:01 |
46|* 4 | HASH JOIN | | 13 | 663 | 7 (15)| 00:00:01 |
47| 5 | TABLE ACCESS FULL| DEPT | 4 | 52 | 3 (0)| 00:00:01 |
48|* 6 | TABLE ACCESS FULL| EMP | 13 | 494 | 3 (0)| 00:00:01 |
49------------------------------------------------------------------------------------
50
51Predicate Information (identified by operation id):
52---------------------------------------------------
53
54 1 - access("V"."DEPTNO"(+)="T"."DEPTNO")
55 4 - access("A"."DEPTNO"="B"."DEPTNO")
56 6 - filter("EMPNO"<>7369)
可见，视图被保留了下来，单独执行。
（三）复杂视图合并（Complex View Merging）
1LHR@orclasm > SELECT * FROM VW_CVM_LHR V,SCOTT.DEPT T WHERE V.JOB=T.DNAME AND V.JOB='DBA';
2
3no rows selected
4
5
6Execution Plan
7----------------------------------------------------------
8Plan hash value: 2922957592
9
10-----------------------------------------------------------------------------------
11| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
12-----------------------------------------------------------------------------------
13| 0 | SELECT STATEMENT | | 1 | 39 | 7 (15)| 00:00:01 |
14|* 1 | HASH JOIN | | 1 | 39 | 7 (15)| 00:00:01 |
15| 2 | VIEW | VW_CVM_LHR | 1 | 19 | 3 (0)| 00:00:01 |
16| 3 | HASH GROUP BY | | 1 | 8 | 3 (0)| 00:00:01 |
17|* 4 | TABLE ACCESS FULL| EMP | 3 | 24 | 3 (0)| 00:00:01 |
18|* 5 | TABLE ACCESS FULL | DEPT | 1 | 20 | 3 (0)| 00:00:01 |
19-----------------------------------------------------------------------------------
20
21Predicate Information (identified by operation id):
22---------------------------------------------------
23
24 1 - access("V"."JOB"="T"."DNAME")
25 4 - filter("T"."JOB"='DBA')
26 5 - filter("T"."DNAME"='DBA')
27
28LHR@orclasm > SELECT /*+MERGE(V)*/ * FROM VW_CVM_LHR V,SCOTT.DEPT T WHERE V.JOB=T.DNAME AND V.JOB='DBA';
29
30no rows selected
31
32
33Execution Plan
34----------------------------------------------------------
35Plan hash value: 2006461124
36
37----------------------------------------------------------------------------
38| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
39----------------------------------------------------------------------------
40| 0 | SELECT STATEMENT | | 1 | 28 | 8 (25)| 00:00:01 |
41| 1 | HASH GROUP BY | | 1 | 28 | 8 (25)| 00:00:01 |
42|* 2 | HASH JOIN | | 3 | 84 | 7 (15)| 00:00:01 |
43|* 3 | TABLE ACCESS FULL| DEPT | 1 | 20 | 3 (0)| 00:00:01 |
44|* 4 | TABLE ACCESS FULL| EMP | 3 | 24 | 3 (0)| 00:00:01 |
45----------------------------------------------------------------------------
46
47Predicate Information (identified by operation id):
48---------------------------------------------------
49
50 2 - access("T"."JOB"="T"."DNAME")
51 3 - filter("T"."DNAME"='DBA')
52 4 - filter("T"."JOB"='DBA')
本文选自《Oracle程序员面试笔试宝典》，作者：李华荣。
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