NoSQL (NoSQL = Not Only SQL ),意即不仅仅是SQL; 指的是非关系型的数据库。随着互联网web2.0网站的兴起,传统的关系数据库在应付web2.0网站,特别是超大规模和高并发的SNS类型的web2.0纯动态网站已经显得力不从心,暴露了很多难以克服的问题,而非关系型
NoSQL
(NoSQL = Not Only SQL ),意即“不仅仅是SQL;
指的是非关系型的数据库。随着互联网web2.0网站的兴起,传统的关系数据库在应付web2.0网站,特别是超大规模和高并发的SNS类型的web2.0纯动态网站已经显得力不从心,暴露了很多难以克服的问题,而非关系型的数据库则由于其本身的特点得到了非常迅速的发展。
为什么是NoSql
1 对数据库高并发读写的需求
2 对海量数据的高效率存储和访问需求
3 对数据库的高可扩展星和高可用性的需求
NoSql特点
它们可以处理超大量的数据。
它们运行在便宜的PC服务器集群上。
它们击碎了性能瓶颈。
没有过多的操作
Bootstrap支持
因为NoSQL项目都是开源的,因此它们缺乏供应商提供的正式支持。这一点它们与大多数开源项目一样,不得不从社区中寻求支持。
优点:
易扩展
大数据量,高性能
灵活性数据模型
NoSQL无需事先为要存储的数据建立字段,随时可以存储自定义的数据格式。而在关系数据库里,增删字段是一件非常麻烦的事情。如果是非常大数据量的表,增加字段简直就是一个噩梦。这点在大数据量的web2.0时代尤其明显。
高可用
缺点:
没有正式的官方支持。
产品层出不穷,并准不定。
以下是NoSql的一些产品截图
初始Mongodb
是一个介于关系数据库和非关系数据库之间的产品,是非关系数据库当中功能最丰富,最像关系数据库的。他支持的
数据结构非常松散,是类似json的bjson格式,因此可以存储比较复杂的数据类型.
1 面向集合
2 模式自由
意味着存储在MOngodb数据库中的文件,我们不需求知道它的任何结构定义。"无模式"是什么概念呢?例如:下面的两个记录可以存在于同一个集合里面:
{"welcome":"beijing"} {"age":25}
怎么样,是不是很像前面学习过的json数据格式呀。也是想c++中的结构体吧。
所以这个学习相同的地方还是有很多的
3 文档型
意思是我们存储的数据类型是键--值对的集合,键是字符串,值可以是数据类型集合里的任务类型,包括数组和文档,我们把这个数据格式称为“BSON”是“Binary serialized Document Notation
"
下面介绍特点和使用场合。
特点:
这里就只说上诉没有提到的
模式自由
面向集合
支持查询
使用高效的二进制数据存储
自动处理碎片
可通过网络访问
适用场合:
网站数据:Mongodb非常适用于适时的插入,更新域查询,并具备实时数据存储所需要的复制及高度伸缩性
缓存:
用于对象及json数据的存储。
以上是Nosql的基本简介。可以看到针对其中的Mongodb的操作以及数据的存储。与Js的Json是没有区别的。而Mongodb的数据操作语法极其类似与SQl。所以这就是老师说的,学习的相通行。

In MySQL, sorting uses the ORDERBY clause, and ranking uses the RANK(), DENSE_RANK(), and ROW_NUMBER() functions. 1. Sort: Use ORDERBY clause, such as SELECT*FROMemployeesORDERBYsalaryDESC; 2. Ranking: Use window functions, such as SELECTemployee_name, salary, RANK()OVER(ORDERBYsalaryDESC)ASrankFROMemployees; these operations are based on SQL query optimizer and execution engine, and are often used to sort quickly or merge sort, and ranking depends on window function calculation.

To create and call stored procedures in MySQL, follow the following steps: 1. Create stored procedures: Use the CREATEPROCEDURE statement to define stored procedures, including names, parameters, and SQL statements. 2. Compile stored procedures: MySQL compiles stored procedures into executable code and stores them. 3. Call stored procedure: use CALL statement and pass parameters. 4. Execute stored procedures: MySQL executes the SQL statements in it, processes parameters and returns the result.

The MySQL service can be set to automatically start on Windows, Linux, and macOS. 1) On Windows, use the command "scconfigmysqlstart=auto" to configure. 2) On Linux, enable it using "sudosystemctlenablemysql". 3) On macOS, create and load the launchd configuration file to achieve automatic startup.

The methods to view the MySQL table structure include: 1. Use the DESCRIBE command to view column information; 2. Use the SHOWCREATETABLE command to view table creation statements; 3. Use information_schema to query more detailed information. These methods help to quickly understand table structure and improve work efficiency.

Installing MySQL on macOS can be achieved through the following steps: 1. Install Homebrew, using the command /bin/bash-c"$(curl-fsSLhttps://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh)". 2. Update Homebrew and use brewupdate. 3. Install MySQL and use brewinstallmysql. 4. Start MySQL service and use brewservicesstartmysql. After installation, you can use mysql-u

In MySQL, conditional filtering is implemented through the WHERE clause and grouping is completed through the GROUPBY clause. 1. Use the WHERE clause to filter data, such as finding employees with salary above 5,000. 2. Use the GROUPBY clause to group and aggregate data, such as counting the number of employees by department. 3. Choose the appropriate index to optimize query performance and avoid using functions or expressions as WHERE conditions. 4. Combining subqueries and EXPLAIN commands improve the efficiency of complex queries.

In MySQL, clearing table data but preserving table structure can be implemented through the TRUNCATETABLE and DELETE commands. 1. The TRUNCATETABLE command quickly deletes all records and resets the self-increment column. 2. The DELETE command deletes data line by line, does not reset the self-increment column, and can delete specific records in combination with the WHERE clause.

Deduplication in MySQL mainly uses DISTINCT and GROUPBY. 1.DISTINCT is used to return unique values, such as SELECTDISTINCTname, ageFROMusers. 2. GROUPBY realizes deduplication through grouping and can perform aggregation operations, such as SELECTid, name, MAX(created_at)aslatest_dateFROMusersGROUPBYname.


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