正则表达式
products表如下:
1. 基本字符匹配
vcrH1NrV+7j2wdDL0cv3o6zWu9KqcHJvZF9uYW1l1tCw/LqswcvL+cvRy/e1xNfWt/u+zb/J0tTBy6OstvhMSUtFyOe5+7K708PNqMXkt/ujrMTHw7TSqsfzcHJvZF9uYW1l0+vL0cv3tcTX1rf70qrN6sirxqXF5KO60rK+zcrHy7XPwsPmtcTA/dfTo6zQ6NKqyrnTwyBMSUtFIA=="JetPack 1000'才可以适配搜索到。
2 使用or进行匹配搜索,可以搜索两个条件,也可以连接多个条件:
3 匹配几个字符之一://这个的意思是说,匹配1 Ton 或者 2 Ton 或者 3 Ton
但是如果写成下面这样又是不对的://这个得意思是匹配1 或者 2 或者 3 Ton的列
4 范围匹配,[1-5] 其实是 [12345]的简写,此外 [0-9],[3-9]都是合法的。
5 匹配特殊字符,匹配特殊字符需要使用//
6 匹配多个实例
重复元素字符:
元字符说明*0个或多个匹配+1个或多个匹配?0个或1个匹配{n}指定数目的匹配{n,}不少于指定数目的匹配{n,m}匹配数目的范围
下面搜索条件的意思是 首先要有一个右括号,接着应该有一个数字,然后是一个空格,再然后是sticks,最后是0个或1个左括号,问号的意思如上表所示
7 字符种类 为了方便工作,可以使用预先定义的字符集,字符集如下:
类说明[:alpha:]任意字符[:blank:]空格和制表符[:cntrl:]ASCII控制字符(从ASCII0到31和127)[:digit:]任意数字同 [0-9][:graph:]任意可打印字符,但不包括空格[:lower:]任意小写字母[:print:]任意可打印字符[:punct:]即不在[:alnum:]又不在[:cntrl:]中的任意字符[:space:]包括空格在内的任意空白字符[:upper:]任意大写字母[:alnum:]任意字母和数字
接下来从表中搜索prod_name中 有连续4个数字的名字:其中[:digit:]表示任意的数字,{4}表示这个数字需要出现4次:
8 定位符在特定的位置搜索
元字符说明^文本开始$文本的结尾[[:<:>:]]词的结尾
下面的语句时查找以数字或者 . 开头的prod_name

InnoDB uses redologs and undologs to ensure data consistency and reliability. 1.redologs record data page modification to ensure crash recovery and transaction persistence. 2.undologs records the original data value and supports transaction rollback and MVCC.

Key metrics for EXPLAIN commands include type, key, rows, and Extra. 1) The type reflects the access type of the query. The higher the value, the higher the efficiency, such as const is better than ALL. 2) The key displays the index used, and NULL indicates no index. 3) rows estimates the number of scanned rows, affecting query performance. 4) Extra provides additional information, such as Usingfilesort prompts that it needs to be optimized.

Usingtemporary indicates that the need to create temporary tables in MySQL queries, which are commonly found in ORDERBY using DISTINCT, GROUPBY, or non-indexed columns. You can avoid the occurrence of indexes and rewrite queries and improve query performance. Specifically, when Usingtemporary appears in EXPLAIN output, it means that MySQL needs to create temporary tables to handle queries. This usually occurs when: 1) deduplication or grouping when using DISTINCT or GROUPBY; 2) sort when ORDERBY contains non-index columns; 3) use complex subquery or join operations. Optimization methods include: 1) ORDERBY and GROUPB

MySQL/InnoDB supports four transaction isolation levels: ReadUncommitted, ReadCommitted, RepeatableRead and Serializable. 1.ReadUncommitted allows reading of uncommitted data, which may cause dirty reading. 2. ReadCommitted avoids dirty reading, but non-repeatable reading may occur. 3.RepeatableRead is the default level, avoiding dirty reading and non-repeatable reading, but phantom reading may occur. 4. Serializable avoids all concurrency problems but reduces concurrency. Choosing the appropriate isolation level requires balancing data consistency and performance requirements.

MySQL is suitable for web applications and content management systems and is popular for its open source, high performance and ease of use. 1) Compared with PostgreSQL, MySQL performs better in simple queries and high concurrent read operations. 2) Compared with Oracle, MySQL is more popular among small and medium-sized enterprises because of its open source and low cost. 3) Compared with Microsoft SQL Server, MySQL is more suitable for cross-platform applications. 4) Unlike MongoDB, MySQL is more suitable for structured data and transaction processing.

MySQL index cardinality has a significant impact on query performance: 1. High cardinality index can more effectively narrow the data range and improve query efficiency; 2. Low cardinality index may lead to full table scanning and reduce query performance; 3. In joint index, high cardinality sequences should be placed in front to optimize query.

The MySQL learning path includes basic knowledge, core concepts, usage examples, and optimization techniques. 1) Understand basic concepts such as tables, rows, columns, and SQL queries. 2) Learn the definition, working principles and advantages of MySQL. 3) Master basic CRUD operations and advanced usage, such as indexes and stored procedures. 4) Familiar with common error debugging and performance optimization suggestions, such as rational use of indexes and optimization queries. Through these steps, you will have a full grasp of the use and optimization of MySQL.

MySQL's real-world applications include basic database design and complex query optimization. 1) Basic usage: used to store and manage user data, such as inserting, querying, updating and deleting user information. 2) Advanced usage: Handle complex business logic, such as order and inventory management of e-commerce platforms. 3) Performance optimization: Improve performance by rationally using indexes, partition tables and query caches.


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