【DB笔试面试614】在Oracle中，和视图相关的查询转换有哪些？
- 2019 年 10 月 10 日
- 笔记
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题目部分
在Oracle中，和视图相关的查询转换有哪些？
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答案部分
（一）简单视图合并
CREATE OR REPLACE VIEW VW_SVM_LHR AS SELECT * FROM SCOTT.EMP WHERE EMPNO<>7369; SELECT * FROM VW_SVM_LHR V WHERE V.JOB='DBA'; Execution Plan ---------------------------------------------------------- Plan hash value: 3956160932 -------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | -------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 3 | 114 | 3 (0)| 00:00:01 | |* 1 | TABLE ACCESS FULL| EMP | 3 | 114 | 3 (0)| 00:00:01 | -------------------------------------------------------------------------- Predicate Information (identified by operation id): --------------------------------------------------- 1 - filter("JOB"='DBA' AND "EMPNO"<>7369) LHR@orclasm > SELECT /*+ NO_MERGE(V)*/ * FROM VW_SVM_LHR V WHERE V.JOB='DBA'; no rows selected Execution Plan ---------------------------------------------------------- Plan hash value: 45352968 --------------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | --------------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 3 | 261 | 3 (0)| 00:00:01 | | 1 | VIEW | VW_SVM_LHR | 3 | 261 | 3 (0)| 00:00:01 | |* 2 | TABLE ACCESS FULL| EMP | 3 | 114 | 3 (0)| 00:00:01 | --------------------------------------------------------------------------------- Predicate Information (identified by operation id): --------------------------------------------------- 2 - filter("JOB"='DBA' AND "EMPNO"<>7369) LHR@orclasm > ALTER SESSION SET "_SIMPLE_VIEW_MERGING"=FALSE; Session altered. LHR@orclasm > SELECT * FROM VW_SVM_LHR V WHERE V.JOB='DBA'; no rows selected Execution Plan ---------------------------------------------------------- Plan hash value: 45352968 --------------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | --------------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 3 | 261 | 3 (0)| 00:00:01 | | 1 | VIEW | VW_SVM_LHR | 3 | 261 | 3 (0)| 00:00:01 | |* 2 | TABLE ACCESS FULL| EMP | 3 | 114 | 3 (0)| 00:00:01 | --------------------------------------------------------------------------------- Predicate Information (identified by operation id): --------------------------------------------------- 2 - filter("JOB"='DBA' AND "EMPNO"<>7369)
（二）外连接视图合并（Outer Join View Merging）
CREATE OR REPLACE VIEW VW_SVM_LHR AS SELECT * FROM SCOTT.EMP WHERE EMPNO<>7369; SELECT * FROM VW_SVM_LHR V,SCOTT.DEPT T WHERE V.DEPTNO=T.DEPTNO(+); --------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | --------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 13 | 754 | 7 (15)| 00:00:01 | |* 1 | HASH JOIN OUTER | | 13 | 754 | 7 (15)| 00:00:01 | |* 2 | TABLE ACCESS FULL| EMP | 13 | 494 | 3 (0)| 00:00:01 | | 3 | TABLE ACCESS FULL| DEPT | 4 | 80 | 3 (0)| 00:00:01 | --------------------------------------------------------------------------- Predicate Information (identified by operation id): --------------------------------------------------- 1 - access("DEPTNO"="T"."DEPTNO"(+)) 2 - filter("EMPNO"<>7369) --视图作为被驱动表： SELECT /*+ FULL(T)*/ * FROM VW_SVM_LHR V,SCOTT.DEPT T WHERE V.DEPTNO(+)=T.DEPTNO; --------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | --------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 13 | 754 | 7 (15)| 00:00:01 | |* 1 | HASH JOIN OUTER | | 13 | 754 | 7 (15)| 00:00:01 | | 2 | TABLE ACCESS FULL| DEPT | 4 | 80 | 3 (0)| 00:00:01 | |* 3 | TABLE ACCESS FULL| EMP | 13 | 494 | 3 (0)| 00:00:01 | --------------------------------------------------------------------------- Predicate Information (identified by operation id): --------------------------------------------------- 1 - access("DEPTNO"(+)="T"."DEPTNO") 3 - filter("EMPNO"(+)<>7369) --视图含有2个表： CREATE 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; SELECT /*+ FULL(T)*/ * FROM VW_SVM2_LHR V,SCOTT.DEPT T WHERE V.DEPTNO(+)=T.DEPTNO; ------------------------------------------------------------------------------------ | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | ------------------------------------------------------------------------------------ | 0 | SELECT STATEMENT | | 13 | 1508 | 10 (10)| 00:00:01 | |* 1 | HASH JOIN OUTER | | 13 | 1508 | 10 (10)| 00:00:01 | | 2 | TABLE ACCESS FULL | DEPT | 4 | 80 | 3 (0)| 00:00:01 | | 3 | VIEW | VW_SVM2_LHR | 13 | 1248 | 7 (15)| 00:00:01 | |* 4 | HASH JOIN | | 13 | 663 | 7 (15)| 00:00:01 | | 5 | TABLE ACCESS FULL| DEPT | 4 | 52 | 3 (0)| 00:00:01 | |* 6 | TABLE ACCESS FULL| EMP | 13 | 494 | 3 (0)| 00:00:01 | ------------------------------------------------------------------------------------ Predicate Information (identified by operation id): --------------------------------------------------- 1 - access("V"."DEPTNO"(+)="T"."DEPTNO") 4 - access("A"."DEPTNO"="B"."DEPTNO") 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）
LHR@orclasm > SELECT * FROM VW_CVM_LHR V,SCOTT.DEPT T WHERE V.JOB=T.DNAME AND V.JOB='DBA'; no rows selected Execution Plan ---------------------------------------------------------- Plan hash value: 2922957592 ----------------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | ----------------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 1 | 39 | 7 (15)| 00:00:01 | |* 1 | HASH JOIN | | 1 | 39 | 7 (15)| 00:00:01 | | 2 | VIEW | VW_CVM_LHR | 1 | 19 | 3 (0)| 00:00:01 | | 3 | HASH GROUP BY | | 1 | 8 | 3 (0)| 00:00:01 | |* 4 | TABLE ACCESS FULL| EMP | 3 | 24 | 3 (0)| 00:00:01 | |* 5 | TABLE ACCESS FULL | DEPT | 1 | 20 | 3 (0)| 00:00:01 | ----------------------------------------------------------------------------------- Predicate Information (identified by operation id): --------------------------------------------------- 1 - access("V"."JOB"="T"."DNAME") 4 - filter("T"."JOB"='DBA') 5 - filter("T"."DNAME"='DBA') LHR@orclasm > SELECT /*+MERGE(V)*/ * FROM VW_CVM_LHR V,SCOTT.DEPT T WHERE V.JOB=T.DNAME AND V.JOB='DBA'; no rows selected Execution Plan ---------------------------------------------------------- Plan hash value: 2006461124 ---------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | ---------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 1 | 28 | 8 (25)| 00:00:01 | | 1 | HASH GROUP BY | | 1 | 28 | 8 (25)| 00:00:01 | |* 2 | HASH JOIN | | 3 | 84 | 7 (15)| 00:00:01 | |* 3 | TABLE ACCESS FULL| DEPT | 1 | 20 | 3 (0)| 00:00:01 | |* 4 | TABLE ACCESS FULL| EMP | 3 | 24 | 3 (0)| 00:00:01 | ---------------------------------------------------------------------------- Predicate Information (identified by operation id): --------------------------------------------------- 2 - access("T"."JOB"="T"."DNAME") 3 - filter("T"."DNAME"='DBA') 4 - filter("T"."JOB"='DBA')
本文选自《Oracle程序员面试笔试宝典》，作者：李华荣。
