In mysql, "case when" is used to calculate a condition list and return one of multiple possible result expressions; "case when" has two syntax formats: 1. Simple function "CASE[col_name]WHEN [value1]THEN[result1]…ELSE[default]END”; 2. Search function “CASE WHEN[expr]THEN[result1]…ELSE[default]END”.
The operating environment of this tutorial: windows10 system, mysql8.0.22 version, Dell G3 computer.
How to use case when in mysql
The case when statement is used to calculate a list of conditions and return one of multiple possible result expressions.
CASE comes in two formats: Simple CASE function compares an expression to a set of simple expressions to determine the result. The CASE search function evaluates a set of Boolean expressions to determine a result. Both formats support the optional ELSE parameter.
When doing data analysis, you need to find data from the database and perform analysis and display. Accurate data query results are conducive to concise and effective analysis in the later period. During this period, case when in mysql was used. Record the usage of case when.
The CASE statement is a multi-branch statement structure. The statement first searches for a value equal to the VALUE after CASE from the VALUE after WHEN. If found, the content of the branch is executed, otherwise the content after ELSE is executed. .
MySql has two case when syntaxes:
1. Simple function
CASE[col_name]WHEN[value1]THEN[result1]…ELSE[default]END
2. Search function
CASE WHEN[expr]THEN[result1]…ELSE[default]END
Simple function
CASE input_expression WHEN when_expression THEN result_expression [...n ] [ ELSE else_result_expression END
Enumerate all possible values of Input_expression.
The data types of Input_expression and each when_expression must be the same, or they must be implicitly converted.
Search function
CASE WHEN [Boolean_expression] THEN [result1]…ELSE [default] END
Judge the Boolean_expression expression, if it is satisfied, return The result after then
Take the personnel table as an example
The first usage, when must be followed by the value of the case column, not an expression
select case sex when sex='1' then '男' when sex='2' then '女' else '其他' end as '性别' from people; select case sex when sex='2' then '女' when sex='1' then '男' else '其他' end as '性别' from people;
Query results
Reason: Because when is followed not by all the possible values of the case column, but by an expression, why does a result like 'male' appear? , need to think about it, and then update it after researching and understanding it later
Correct writing
select case sex when '1' then '男' when '2' then '女' else '其他' end as '性别' from people;
Query results
Recommended learning:mysql Video tutorial
The above is the detailed content of How to use mysql case when. For more information, please follow other related articles on the PHP Chinese website!

本篇文章给大家带来了关于mysql的相关知识,其中主要介绍了关于架构原理的相关内容,MySQL Server架构自顶向下大致可以分网络连接层、服务层、存储引擎层和系统文件层,下面一起来看一下,希望对大家有帮助。

在mysql中,可以利用char()和REPLACE()函数来替换换行符;REPLACE()函数可以用新字符串替换列中的换行符,而换行符可使用“char(13)”来表示,语法为“replace(字段名,char(13),'新字符串') ”。

mysql的msi与zip版本的区别:1、zip包含的安装程序是一种主动安装,而msi包含的是被installer所用的安装文件以提交请求的方式安装;2、zip是一种数据压缩和文档存储的文件格式,msi是微软格式的安装包。

方法:1、利用right函数,语法为“update 表名 set 指定字段 = right(指定字段, length(指定字段)-1)...”;2、利用substring函数,语法为“select substring(指定字段,2)..”。

转换方法:1、利用cast函数,语法“select * from 表名 order by cast(字段名 as SIGNED)”;2、利用“select * from 表名 order by CONVERT(字段名,SIGNED)”语句。

本篇文章给大家带来了关于mysql的相关知识,其中主要介绍了关于MySQL复制技术的相关问题,包括了异步复制、半同步复制等等内容,下面一起来看一下,希望对大家有帮助。

本篇文章给大家带来了关于mysql的相关知识,其中主要介绍了mysql高级篇的一些问题,包括了索引是什么、索引底层实现等等问题,下面一起来看一下,希望对大家有帮助。

在mysql中,可以利用REGEXP运算符判断数据是否是数字类型,语法为“String REGEXP '[^0-9.]'”;该运算符是正则表达式的缩写,若数据字符中含有数字时,返回的结果是true,反之返回的结果是false。


Hot AI Tools

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

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

Undress AI Tool
Undress images for free

Clothoff.io
AI clothes remover

AI Hentai Generator
Generate AI Hentai for free.

Hot Article

Hot Tools

ZendStudio 13.5.1 Mac
Powerful PHP integrated development environment

SAP NetWeaver Server Adapter for Eclipse
Integrate Eclipse with SAP NetWeaver application server.

EditPlus Chinese cracked version
Small size, syntax highlighting, does not support code prompt function

DVWA
Damn Vulnerable Web App (DVWA) is a PHP/MySQL web application that is very vulnerable. Its main goals are to be an aid for security professionals to test their skills and tools in a legal environment, to help web developers better understand the process of securing web applications, and to help teachers/students teach/learn in a classroom environment Web application security. The goal of DVWA is to practice some of the most common web vulnerabilities through a simple and straightforward interface, with varying degrees of difficulty. Please note that this software

Atom editor mac version download
The most popular open source editor
