How to implement ascending query in mysql
In mysql, you can use the "SELECT" statement and the "ORDER BY" keyword to implement ascending query, the syntax "SELECT {*|field column name} FROM table name [WHERE condition] GROUP BY field name ASC; ".
The operating environment of this tutorial: windows7 system, mysql8 version, Dell G3 computer.
In mysql, you can use the "SELECT" statement and the "ORDER BY" keyword to implement ascending query.
The SELECT statement is used to query data, and the ORDER BY keyword is mainly used to sort the data in the query results in a certain order.
Basic syntax:
SELECT {*|字段列名} FROM 表名 [WHERE 条件] GROUP BY 字段名 [ASC|DESC];
The syntax is explained below.
Field name: Indicates the name of the field that needs to be sorted. If there are multiple fields, separate them with commas.
ASC|DESC: ASC indicates that the fields are sorted in ascending order; DESC indicates that the fields are sorted in descending order. ASC is the default value.
When using the ORDER BY keyword, you should pay attention to the following aspects:
The ORDER BY keyword can be followed by a subquery (about the subquery) The tutorial will explain it in detail, just learn it here).
When there is a null value in the sorted field, ORDER BY will treat the null value as the minimum value.
ORDER BY When specifying multiple fields for sorting, MySQL will sort from left to right according to the order of the fields.
Single field sorting
The following uses a specific example to illustrate that when ORDER BY specifies a single field, MySQL How to sort query results.
Example 1
The following queries all records in the tb_students_info table and sorts the height field. The SQL statement and running results are as follows.
mysql> SELECT * FROM tb_students_info ORDER BY height; +----+--------+---------+------+------+--------+------------+ | id | name | dept_id | age | sex | height | login_date | +----+--------+---------+------+------+--------+------------+ | 2 | Green | 3 | 23 | F | 158 | 2016-10-22 | | 1 | Dany | 1 | 25 | F | 160 | 2015-09-10 | | 4 | Jane | 1 | 22 | F | 162 | 2016-12-20 | | 7 | Lily | 6 | 22 | F | 165 | 2016-02-26 | | 10 | Tom | 4 | 23 | M | 165 | 2016-08-05 | | 8 | Susan | 4 | 23 | F | 170 | 2015-10-01 | | 6 | John | 2 | 21 | M | 172 | 2015-11-11 | | 5 | Jim | 1 | 24 | M | 175 | 2016-01-15 | | 9 | Thomas | 3 | 22 | M | 178 | 2016-06-07 | | 3 | Henry | 2 | 23 | M | 185 | 2015-05-31 | +----+--------+---------+------+------+--------+------------+ 10 rows in set (0.08 sec)
As you can see from the results, MySQL sorts the data in the height field of the query in ascending order according to the size of the value.
Multi-field sorting
The following uses a specific example to illustrate how MySQL performs query results when ORDER BY specifies multiple fields. Sort.
Example 2
Query the name and height fields in the tb_students_info table, sort by height first, and then by name. The SQL statement and running results are as follows.
mysql> SELECT name,height FROM tb_students_info ORDER BY height,name; +--------+--------+ | name | height | +--------+--------+ | Green | 158 | | Dany | 160 | | Jane | 162 | | Lily | 165 | | Tom | 165 | | Susan | 170 | | John | 172 | | Jim | 175 | | Thomas | 178 | | Henry | 185 | +--------+--------+ 10 rows in set (0.09 sec)
Note: When sorting multiple fields, the first field to be sorted must have the same value before the second field is sorted. If all values in the first field's data are unique, MySQL will no longer sort the second field.
By default, the query data is sorted in ascending alphabetical order (A~Z), but the sorting of data is not limited to this. You can also use DESC in ORDER BY to sort the query results in descending order (Z~A ).
Example 3
Query the tb_students_info table, first sort by height in descending order, and then by name in ascending order. The SQL statement and running results are as follows.
mysql> SELECT name,height FROM tb_student_info ORDER BY height DESC,name ASC; +--------+--------+ | name | height | +--------+--------+ | Henry | 185 | | Thomas | 178 | | Jim | 175 | | John | 172 | | Susan | 170 | | Lily | 165 | | Tom | 165 | | Jane | 162 | | Dany | 160 | | Green | 158 | +--------+--------+ 10 rows in set (0.00 sec)
DESC keyword only sorts the previous columns in descending order, here only the height field is sorted in descending order. Therefore, height is sorted in descending order, while name is still sorted in ascending order. If you want to sort in descending order on multiple columns, you must specify the DESC keyword for each column.
[Related recommendations: mysql video tutorial]
The above is the detailed content of How to implement ascending query in mysql. For more information, please follow other related articles on the PHP Chinese website!

Hot AI Tools

Undress AI Tool
Undress images for free

Undresser.AI Undress
AI-powered app for creating realistic nude photos

AI Clothes Remover
Online AI tool for removing clothes from photos.

Clothoff.io
AI clothes remover

Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!

Hot Article

Hot Tools

Notepad++7.3.1
Easy-to-use and free code editor

SublimeText3 Chinese version
Chinese version, very easy to use

Zend Studio 13.0.1
Powerful PHP integrated development environment

Dreamweaver CS6
Visual web development tools

SublimeText3 Mac version
God-level code editing software (SublimeText3)

Hot Topics

1. The first choice for the Laravel MySQL Vue/React combination in the PHP development question and answer community is the first choice for Laravel MySQL Vue/React combination, due to its maturity in the ecosystem and high development efficiency; 2. High performance requires dependence on cache (Redis), database optimization, CDN and asynchronous queues; 3. Security must be done with input filtering, CSRF protection, HTTPS, password encryption and permission control; 4. Money optional advertising, member subscription, rewards, commissions, knowledge payment and other models, the core is to match community tone and user needs.

There are three ways to connect Excel to MySQL database: 1. Use PowerQuery: After installing the MySQLODBC driver, establish connections and import data through Excel's built-in PowerQuery function, and support timed refresh; 2. Use MySQLforExcel plug-in: The official plug-in provides a friendly interface, supports two-way synchronization and table import back to MySQL, and pay attention to version compatibility; 3. Use VBA ADO programming: suitable for advanced users, and achieve flexible connections and queries by writing macro code. Choose the appropriate method according to your needs and technical level. PowerQuery or MySQLforExcel is recommended for daily use, and VBA is better for automated processing.

To achieve MySQL deployment automation, the key is to use Terraform to define resources, Ansible management configuration, Git for version control, and strengthen security and permission management. 1. Use Terraform to define MySQL instances, such as the version, type, access control and other resource attributes of AWSRDS; 2. Use AnsiblePlaybook to realize detailed configurations such as database user creation, permission settings, etc.; 3. All configuration files are included in Git management, support change tracking and collaborative development; 4. Avoid hard-coded sensitive information, use Vault or AnsibleVault to manage passwords, and set access control and minimum permission principles.

There are three main ways to set environment variables in PHP: 1. Global configuration through php.ini; 2. Passed through a web server (such as SetEnv of Apache or fastcgi_param of Nginx); 3. Use putenv() function in PHP scripts. Among them, php.ini is suitable for global and infrequently changing configurations, web server configuration is suitable for scenarios that need to be isolated, and putenv() is suitable for temporary variables. Persistence policies include configuration files (such as php.ini or web server configuration), .env files are loaded with dotenv library, and dynamic injection of variables in CI/CD processes. Security management sensitive information should be avoided hard-coded, and it is recommended to use.en

To collect user behavior data, you need to record browsing, search, purchase and other information into the database through PHP, and clean and analyze it to explore interest preferences; 2. The selection of recommendation algorithms should be determined based on data characteristics: based on content, collaborative filtering, rules or mixed recommendations; 3. Collaborative filtering can be implemented in PHP to calculate user cosine similarity, select K nearest neighbors, weighted prediction scores and recommend high-scoring products; 4. Performance evaluation uses accuracy, recall, F1 value and CTR, conversion rate and verify the effect through A/B tests; 5. Cold start problems can be alleviated through product attributes, user registration information, popular recommendations and expert evaluations; 6. Performance optimization methods include cached recommendation results, asynchronous processing, distributed computing and SQL query optimization, thereby improving recommendation efficiency and user experience.

PHP plays the role of connector and brain center in intelligent customer service, responsible for connecting front-end input, database storage and external AI services; 2. When implementing it, it is necessary to build a multi-layer architecture: the front-end receives user messages, the PHP back-end preprocesses and routes requests, first matches the local knowledge base, and misses, call external AI services such as OpenAI or Dialogflow to obtain intelligent reply; 3. Session management is written to MySQL and other databases by PHP to ensure context continuity; 4. Integrated AI services need to use Guzzle to send HTTP requests, safely store APIKeys, and do a good job of error handling and response analysis; 5. Database design must include sessions, messages, knowledge bases, and user tables, reasonably build indexes, ensure security and performance, and support robot memory

To enable PHP containers to support automatic construction, the core lies in configuring the continuous integration (CI) process. 1. Use Dockerfile to define the PHP environment, including basic image, extension installation, dependency management and permission settings; 2. Configure CI/CD tools such as GitLabCI, and define the build, test and deployment stages through the .gitlab-ci.yml file to achieve automatic construction, testing and deployment; 3. Integrate test frameworks such as PHPUnit to ensure that tests are automatically run after code changes; 4. Use automated deployment strategies such as Kubernetes to define deployment configuration through the deployment.yaml file; 5. Optimize Dockerfile and adopt multi-stage construction

To recycle MySQL user permissions using REVOKE, you need to specify the permission type, database, and user by format. 1. Use REVOKEALLPRIVILEGES, GRANTOPTIONFROM'username'@'hostname'; 2. Use REVOKEALLPRIVILEGESONmydb.FROM'username'@'hostname'; 3. Use REVOKEALLPRIVILEGESONmydb.FROM'username'@'hostname'; 3. Use REVOKE permission type ON.*FROM'username'@'hostname'; Note that after execution, it is recommended to refresh the permissions. The scope of the permissions must be consistent with the authorization time, and non-existent permissions cannot be recycled.
