- 浏览: 453525 次
- 性别:
- 来自: 北京
文章分类
最新评论
-
zhengch00:
这个文档不是你自己写的吧
informatica连接ftp -
ctcwri:
于我心有慽慽焉,java的web就像陷入了泥坑。
Java 的纯真年代已经离我们越来越远了 -
bestxiaok:
Glorin 写道这个应该是你的安装目录tomcat文件夹下面 ...
Value must be an existing directory配置tomcat问题? -
Glorin:
这个应该是你的安装目录tomcat文件夹下面少了一个temp文 ...
Value must be an existing directory配置tomcat问题? -
bestxiaok:
sheep3600 写道bestxiaok 写道sheep36 ...
AES加密解密
大家在做SQL优化的过程中,可能都知道一个事实:某些情况下使用UNION替换OR可以提高SQL的运行效率。
您知道这个“某些情况”指的是什么么?
解释一下,“某些情况”指的是:使用的表字段要有索引。
这个实验,给大家展示一下这个结论
1.创建测试表
sec@ora10g> drop table t;
Table dropped.
sec@ora10g> create table t as select * from all_objects;
Table created.
sec@ora10g> alter table t rename column owner to x;
Table altered.
sec@ora10g> alter table t rename column object_name to y;
Table altered.
sec@ora10g> update t set x = 'secooler';
4785 rows updated.
OK,通过上面的初始化,我们得到了这个测试表T,我们关心它的第一个和第二个字段,修改名字后是x字段和y字段
x字段内容统一修改为“secooler”,以便模拟使用这个字段得到大量返回结果
y字段指定特定值后,模拟返回一条记录
2.开启autotrace,跟踪不同的SQL执行(为使执行计划稳定,请多次执行,得到稳定输出结果)
用到的测试SQL语句是以下三条
1)返回记录多的条件放在where子句的前面
select * from t where x = 'secooler' or y = 'T';
2)返回记录多的条件放在where子句的后面
select * from t where y = 'T' or x = 'secooler';
3)使用UNION改写上面的OR语句
select * from t where x = 'secooler'
union
select * from t where y = 'T'
/
3.先看一下,在没有创建索引情况下的实验效果
sec@ora10g> set autotrace traceonly
sec@ora10g> select * from t where x = 'secooler' or y = 'T';
4782 rows selected.
Execution Plan
----------------------------------------------------------
Plan hash value: 1601196873
--------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 4583 | 572K| 16 (0)| 00:00:01 |
|* 1 | TABLE ACCESS FULL| T | 4583 | 572K| 16 (0)| 00:00:01 |
--------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter("X"='secooler' OR "Y"='T')
Note
-----
- dynamic sampling used for this statement
Statistics
----------------------------------------------------------
0 recursive calls
0 db block gets
111 consistent gets
0 physical reads
0 redo size
206142 bytes sent via SQL*Net to client
1009 bytes received via SQL*Net from client
49 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
4782 rows processed
sec@ora10g> select * from t where y = 'T' or x = 'secooler';
4782 rows selected.
Execution Plan
----------------------------------------------------------
Plan hash value: 1601196873
--------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 4583 | 572K| 16 (0)| 00:00:01 |
|* 1 | TABLE ACCESS FULL| T | 4583 | 572K| 16 (0)| 00:00:01 |
--------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter("Y"='T' OR "X"='secooler')
Note
-----
- dynamic sampling used for this statement
Statistics
----------------------------------------------------------
0 recursive calls
0 db block gets
111 consistent gets
0 physical reads
0 redo size
206142 bytes sent via SQL*Net to client
1009 bytes received via SQL*Net from client
49 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
4782 rows processed
sec@ora10g> select * from t where x = 'secooler'
union
select * from t where y = 'T'
/
2 3 4
4782 rows selected.
Execution Plan
----------------------------------------------------------
Plan hash value: 2618920678
------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes |TempSpc| Cost (%CPU)| Time |
------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 4584 | 573K| | 168 (12)| 00:00:03 |
| 1 | SORT UNIQUE | | 4584 | 573K| 1448K| 168 (12)| 00:00:03 |
| 2 | UNION-ALL | | | | | | |
|* 3 | TABLE ACCESS FULL| T | 4583 | 572K| | 16 (0)| 00:00:01 |
|* 4 | TABLE ACCESS FULL| T | 1 | 128 | | 16 (0)| 00:00:01 |
------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
3 - filter("X"='secooler')
4 - filter("Y"='T')
Note
-----
- dynamic sampling used for this statement
Statistics
----------------------------------------------------------
0 recursive calls
0 db block gets
126 consistent gets
0 physical reads
0 redo size
253890 bytes sent via SQL*Net to client
1009 bytes received via SQL*Net from client
49 SQL*Net roundtrips to/from client
1 sorts (memory)
0 sorts (disk)
4782 rows processed
4.在没有创建索引情况下的实验结论
1)无论是返回记录多的条件放在where子句的前面还是后面,从执行计划上看,效率是一样的。
2)没有创建索引的情况下,使用UNION改写后效率没有提高,反而下降了
5.在看一下,创建所需的索引情况后的实验效果
sec@ora10g> create index idx1_t on t(x);
Index created.
sec@ora10g> create index idx2_t on t(y);
Index created.
sec@ora10g> select * from t where x = 'secooler' or y = 'T';
4782 rows selected.
Execution Plan
----------------------------------------------------------
Plan hash value: 1601196873
--------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 4583 | 572K| 16 (0)| 00:00:01 |
|* 1 | TABLE ACCESS FULL| T | 4583 | 572K| 16 (0)| 00:00:01 |
--------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter("X"='secooler' OR "Y"='T')
Note
-----
- dynamic sampling used for this statement
Statistics
----------------------------------------------------------
0 recursive calls
0 db block gets
111 consistent gets
0 physical reads
0 redo size
206142 bytes sent via SQL*Net to client
1009 bytes received via SQL*Net from client
49 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
4782 rows processed
sec@ora10g> select * from t where y = 'T' or x = 'secooler';
4782 rows selected.
Execution Plan
----------------------------------------------------------
Plan hash value: 1601196873
--------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 4583 | 572K| 16 (0)| 00:00:01 |
|* 1 | TABLE ACCESS FULL| T | 4583 | 572K| 16 (0)| 00:00:01 |
--------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter("Y"='T' OR "X"='secooler')
Note
-----
- dynamic sampling used for this statement
Statistics
----------------------------------------------------------
0 recursive calls
0 db block gets
111 consistent gets
0 physical reads
0 redo size
206142 bytes sent via SQL*Net to client
1009 bytes received via SQL*Net from client
49 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
4782 rows processed
sec@ora10g> select * from t where x = 'secooler'
union
select * from t where y = 'T'
/
2 3 4
4782 rows selected.
Execution Plan
----------------------------------------------------------
Plan hash value: 4276936497
------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes |TempSpc| Cost (%CPU)| Time |
------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 4584 | 573K| | 153 (3)| 00:00:02 |
| 1 | SORT UNIQUE | | 4584 | 573K| 1448K| 153 (3)| 00:00:02 |
| 2 | UNION-ALL | | | | | | |
|* 3 | TABLE ACCESS FULL | T | 4583 | 572K| | 16 (0)| 00:00:01 |
| 4 | TABLE ACCESS BY INDEX ROWID| T | 1 | 128 | | 2 (0)| 00:00:01 |
|* 5 | INDEX RANGE SCAN | IDX2_T | 1 | | | 1 (0)| 00:00:01 |
------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
3 - filter("X"='secooler')
5 - access("Y"='T')
Note
-----
- dynamic sampling used for this statement
Statistics
----------------------------------------------------------
0 recursive calls
0 db block gets
66 consistent gets
0 physical reads
0 redo size
253890 bytes sent via SQL*Net to client
1009 bytes received via SQL*Net from client
49 SQL*Net roundtrips to/from client
1 sorts (memory)
0 sorts (disk)
4782 rows processed
6.在创建所需的索引后的实验结果
1)无论是返回记录多的条件放在where子句的前面还是后面,从执行计划上看,效率还是一样的。
2)从“consistent gets”参数上看,使用UNION改写OR后,效率得到有效的提升。
7.小结
通过上面的实验,可以得到在CBO模式下,无论是返回记录多的条件放在where子句的前面还是后面,从执行计划上看,效率是一样的。
另外一个重要结论就是:在考虑使用UNION改写OR的时候,一定要注意查看使用的字段是否已经创建了索引。
您知道这个“某些情况”指的是什么么?
解释一下,“某些情况”指的是:使用的表字段要有索引。
这个实验,给大家展示一下这个结论
1.创建测试表
sec@ora10g> drop table t;
Table dropped.
sec@ora10g> create table t as select * from all_objects;
Table created.
sec@ora10g> alter table t rename column owner to x;
Table altered.
sec@ora10g> alter table t rename column object_name to y;
Table altered.
sec@ora10g> update t set x = 'secooler';
4785 rows updated.
OK,通过上面的初始化,我们得到了这个测试表T,我们关心它的第一个和第二个字段,修改名字后是x字段和y字段
x字段内容统一修改为“secooler”,以便模拟使用这个字段得到大量返回结果
y字段指定特定值后,模拟返回一条记录
2.开启autotrace,跟踪不同的SQL执行(为使执行计划稳定,请多次执行,得到稳定输出结果)
用到的测试SQL语句是以下三条
1)返回记录多的条件放在where子句的前面
select * from t where x = 'secooler' or y = 'T';
2)返回记录多的条件放在where子句的后面
select * from t where y = 'T' or x = 'secooler';
3)使用UNION改写上面的OR语句
select * from t where x = 'secooler'
union
select * from t where y = 'T'
/
3.先看一下,在没有创建索引情况下的实验效果
sec@ora10g> set autotrace traceonly
sec@ora10g> select * from t where x = 'secooler' or y = 'T';
4782 rows selected.
Execution Plan
----------------------------------------------------------
Plan hash value: 1601196873
--------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 4583 | 572K| 16 (0)| 00:00:01 |
|* 1 | TABLE ACCESS FULL| T | 4583 | 572K| 16 (0)| 00:00:01 |
--------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter("X"='secooler' OR "Y"='T')
Note
-----
- dynamic sampling used for this statement
Statistics
----------------------------------------------------------
0 recursive calls
0 db block gets
111 consistent gets
0 physical reads
0 redo size
206142 bytes sent via SQL*Net to client
1009 bytes received via SQL*Net from client
49 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
4782 rows processed
sec@ora10g> select * from t where y = 'T' or x = 'secooler';
4782 rows selected.
Execution Plan
----------------------------------------------------------
Plan hash value: 1601196873
--------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 4583 | 572K| 16 (0)| 00:00:01 |
|* 1 | TABLE ACCESS FULL| T | 4583 | 572K| 16 (0)| 00:00:01 |
--------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter("Y"='T' OR "X"='secooler')
Note
-----
- dynamic sampling used for this statement
Statistics
----------------------------------------------------------
0 recursive calls
0 db block gets
111 consistent gets
0 physical reads
0 redo size
206142 bytes sent via SQL*Net to client
1009 bytes received via SQL*Net from client
49 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
4782 rows processed
sec@ora10g> select * from t where x = 'secooler'
union
select * from t where y = 'T'
/
2 3 4
4782 rows selected.
Execution Plan
----------------------------------------------------------
Plan hash value: 2618920678
------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes |TempSpc| Cost (%CPU)| Time |
------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 4584 | 573K| | 168 (12)| 00:00:03 |
| 1 | SORT UNIQUE | | 4584 | 573K| 1448K| 168 (12)| 00:00:03 |
| 2 | UNION-ALL | | | | | | |
|* 3 | TABLE ACCESS FULL| T | 4583 | 572K| | 16 (0)| 00:00:01 |
|* 4 | TABLE ACCESS FULL| T | 1 | 128 | | 16 (0)| 00:00:01 |
------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
3 - filter("X"='secooler')
4 - filter("Y"='T')
Note
-----
- dynamic sampling used for this statement
Statistics
----------------------------------------------------------
0 recursive calls
0 db block gets
126 consistent gets
0 physical reads
0 redo size
253890 bytes sent via SQL*Net to client
1009 bytes received via SQL*Net from client
49 SQL*Net roundtrips to/from client
1 sorts (memory)
0 sorts (disk)
4782 rows processed
4.在没有创建索引情况下的实验结论
1)无论是返回记录多的条件放在where子句的前面还是后面,从执行计划上看,效率是一样的。
2)没有创建索引的情况下,使用UNION改写后效率没有提高,反而下降了
5.在看一下,创建所需的索引情况后的实验效果
sec@ora10g> create index idx1_t on t(x);
Index created.
sec@ora10g> create index idx2_t on t(y);
Index created.
sec@ora10g> select * from t where x = 'secooler' or y = 'T';
4782 rows selected.
Execution Plan
----------------------------------------------------------
Plan hash value: 1601196873
--------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 4583 | 572K| 16 (0)| 00:00:01 |
|* 1 | TABLE ACCESS FULL| T | 4583 | 572K| 16 (0)| 00:00:01 |
--------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter("X"='secooler' OR "Y"='T')
Note
-----
- dynamic sampling used for this statement
Statistics
----------------------------------------------------------
0 recursive calls
0 db block gets
111 consistent gets
0 physical reads
0 redo size
206142 bytes sent via SQL*Net to client
1009 bytes received via SQL*Net from client
49 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
4782 rows processed
sec@ora10g> select * from t where y = 'T' or x = 'secooler';
4782 rows selected.
Execution Plan
----------------------------------------------------------
Plan hash value: 1601196873
--------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 4583 | 572K| 16 (0)| 00:00:01 |
|* 1 | TABLE ACCESS FULL| T | 4583 | 572K| 16 (0)| 00:00:01 |
--------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter("Y"='T' OR "X"='secooler')
Note
-----
- dynamic sampling used for this statement
Statistics
----------------------------------------------------------
0 recursive calls
0 db block gets
111 consistent gets
0 physical reads
0 redo size
206142 bytes sent via SQL*Net to client
1009 bytes received via SQL*Net from client
49 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
4782 rows processed
sec@ora10g> select * from t where x = 'secooler'
union
select * from t where y = 'T'
/
2 3 4
4782 rows selected.
Execution Plan
----------------------------------------------------------
Plan hash value: 4276936497
------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes |TempSpc| Cost (%CPU)| Time |
------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 4584 | 573K| | 153 (3)| 00:00:02 |
| 1 | SORT UNIQUE | | 4584 | 573K| 1448K| 153 (3)| 00:00:02 |
| 2 | UNION-ALL | | | | | | |
|* 3 | TABLE ACCESS FULL | T | 4583 | 572K| | 16 (0)| 00:00:01 |
| 4 | TABLE ACCESS BY INDEX ROWID| T | 1 | 128 | | 2 (0)| 00:00:01 |
|* 5 | INDEX RANGE SCAN | IDX2_T | 1 | | | 1 (0)| 00:00:01 |
------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
3 - filter("X"='secooler')
5 - access("Y"='T')
Note
-----
- dynamic sampling used for this statement
Statistics
----------------------------------------------------------
0 recursive calls
0 db block gets
66 consistent gets
0 physical reads
0 redo size
253890 bytes sent via SQL*Net to client
1009 bytes received via SQL*Net from client
49 SQL*Net roundtrips to/from client
1 sorts (memory)
0 sorts (disk)
4782 rows processed
6.在创建所需的索引后的实验结果
1)无论是返回记录多的条件放在where子句的前面还是后面,从执行计划上看,效率还是一样的。
2)从“consistent gets”参数上看,使用UNION改写OR后,效率得到有效的提升。
7.小结
通过上面的实验,可以得到在CBO模式下,无论是返回记录多的条件放在where子句的前面还是后面,从执行计划上看,效率是一样的。
另外一个重要结论就是:在考虑使用UNION改写OR的时候,一定要注意查看使用的字段是否已经创建了索引。
发表评论
-
JAVA 程序中使用ORACLE 绑定变量( bind variable )
2012-08-17 10:45 28901、为什么要使用绑定变量 (1)SQL语 句硬分 ... -
ArrayList的性能优化
2012-06-13 19:56 2099size、isEmpty、get、set、iterat ... -
oracle加 行锁
2012-06-13 13:19 1658加锁是为了防止一些操作而进行的,比如说共享锁,可以防止 ... -
java支持的最大内存
2012-06-13 11:14 17871、jdk各个版本在不同操作系统中支持的最大内存是不一样的,但 ... -
update多列更新
2012-04-05 16:06 1955再ETL的时候,经常会遇到列转换的问题,再对照转换中出现多列更 ... -
oracle数据库间数据快速 复制
2012-03-26 15:59 1994一种利用dblink模式: 1 Create public ... -
Java 的纯真年代已经离我们越来越远了
2012-03-07 15:05 1514[size=medium]用Java 去写跨 ... -
unable to access jarfile ***.jar
2012-02-28 10:52 2382相信有不少朋友遇到过这样的问题——如题,我今天也遇到了,后来发 ... -
Can't open a connection to site 'SYB_BACKUP' 解决办法
2012-02-08 10:56 2063把可能遇到的情况总结一下: 1、出错该错误可以先检查一下Syb ... -
AES加密解密
2012-01-06 16:48 2031由于刚才的方法不好使,算出来的东西不知道是什么进制,整迷糊了, ... -
java 加密解密 算法1
2012-01-06 15:44 1821采用对称的加密的算法 ... -
数据库知识:Oracle服务的知识详解
2012-01-06 14:40 1156Oracle数据库的操作中, ... -
update 多表更新
2011-11-09 15:35 1016在开发中,数据库来回换,而有些关键性的语法又各不相同,这是一件 ... -
ora-00957:duplicate column name
2011-11-07 16:49 2429ora-00957:duplicate column name ... -
ResultSet获取行数
2011-11-06 11:21 1541网上有人说用这种方式获取: ResultSet里面有,你先把r ... -
java.lang.ArrayIndexOutOfBoundsException: 6
2011-11-06 11:11 4454java.lang.ArrayIndexOutOfBounds ... -
Oracle: ORA-01000: 超出打开游标的最大数问题
2011-11-02 09:53 1786java.sql.SQLException: ORA-0100 ... -
几种常用的数据库分页
2011-11-01 22:33 12131.oracle数据库分页 select * from (se ... -
查看当前数据库全表扫描的SQL
2011-07-22 16:07 2118在大数据操作表的时候经常会遇到查询慢的问题,有的时候的确是数据 ... -
oracle flashback闪回技术
2011-07-21 16:13 950今天在操作数据库的时候,由于登陆的时候没有认真看数据库名,导致 ...
相关推荐
- 对于两个索引列,UNION通常比OR有更高的效率。 - IS NULL操作会破坏索引,可以考虑其他方式来处理空值。 9. **避免不必要的操作**: - DISTINCT、UNION、MINUS、INTERSECT和ORDER BY等操作都会涉及排序,消耗...
可以尝试使用`UNION ALL`来代替`OR`,以提高查询效率。 - **案例**:将`SELECT * FROM t WHERE num = 10 OR num = 20`修改为`SELECT * FROM t WHERE num = 10 UNION ALL SELECT * FROM t WHERE num = 20`。 **5. ...
6. **避免`OR`与`UNION`**:在`JOIN`操作中,尽量避免在`WHERE`子句中使用`OR`,可能的话,用`UNION`来替换,因为`UNION`更容易优化。 7. **避免函数与表达式**:在索引字段上使用函数(如`UPPER(field)`)会导致...
这里使用了异或运算符`^`来替换单引号,从而绕过过滤机制。 **实战技巧** 1. **了解异或操作**:熟悉异或操作的特性和如何在SQL注入中利用它。 2. **多种绕过技巧**:尝试结合使用多种技术来实现注入。 3. **测试...
- 避免在`WHERE`子句中使用`OR`,可以考虑使用`UNION ALL`替代。 - 使用`JOIN`时,确保关联条件是索引,且数据量较小的一方作为驱动表。 3. **SQL语句重构**: - 避免在循环中执行单条SQL,改为一次性处理多条...
- **建议6.7 用UNION替换OR(适用于索引列)**:在某些情况下,使用UNION可以提高查询效率。 - **建议6.8 如何删除重复记录**:通过使用临时表或其他技术手段来高效地删除重复记录。 - **建议6.9 用TRUNCATE替代DELETE...
- **解决方案**:使用 `UNION ALL` 替换 `OR`,可以更高效地处理多个独立的查询。 **5. 避免使用 `LIKE` 开头的通配符** - **问题分析**:使用 `%` 开头的 `LIKE` 语句(例如 `LIKE '%abc%'`)通常会导致全表...
它不仅支持多种编程语言的语法高亮显示,还具备代码折叠、自动完成等功能,极大地提高了程序员的工作效率。然而,默认情况下,EditPlus并不直接支持SQL(Structured Query Language)这种数据库查询语言。 #### 二...
8. **使用`UNION ALL`**:在某些情况下,将`DISTINCT`替换为多个`UNION ALL`子查询可能更有效,因为`UNION ALL`不进行去重操作,只合并结果集。 在实际应用中,优化SQL查询需要根据具体的数据库结构、数据分布和...
一种常见的方法是使用编辑距离(Levenshtein Distance),它计算将一个字符串转换为另一个字符串所需的最少单字符编辑(插入、删除或替换)次数。 接下来,我们可以利用Python的内置数据结构,如列表和字典,来实现...
面向对象的软件工程是面向对象方法在软件工程领域的全面应用,它包括面向对象的分析(OOA)、面向对象的设计(OOD)、面向对象的编程(OOP)、面向对象的测试(OOT)和面向对象的软件维护(OOSM)等主要内容。...