Mysql's case the when you how to use

How to use mysql's case when

This article introduces the knowledge of "how to use the case when of mysql". During the operation of the actual case,Many people will encounter such dilemmas, and then let Xiaobian lead you to learn how to deal with these situations!I hope you read it carefully and learn something!

In mysql, "case when" is used to evaluate a list of conditions 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 mysql's case when

The

case when statement evaluates a list of conditions and returns one of several possible result expressions.

CASE has two formats: The 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 the result.Both formats support an optional ELSE parameter.

When doing data analysis, it is necessary to find data from the database and analyze and display it. Accurate data query results are conducive to concise and effective analysis in the later stage.During this period, the case when in mysql was used, and the usage of case when was recorded.

CASE statement is a multi-branch statement structure. The statement first searches for the value equal to the VALUE after CASE from the VALUE after WHEN. If it is found, execute the content of the branch, otherwise execute the content after ELSE.

MySql's case when syntax has two types:

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_expressionWHEN when_expression THEN result_expression [...n ] [ELSE  else_result_expressionEND

Enumerates all possible values ​​of Input_expression.

Input_expression and each when_expression must have the same data type, or be implicitly converted.

Search function

CASE WHEN [Boolean_expression] THEN [result1]…ELSE [default] END

Judging the Boolean_expression expression, if 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 'male' when sex='2' then 'female' else 'other' end as 'gender' from people;select case sex when sex='2' then 'female' when sex='1' then 'male' else 'other' end as 'gender' from people;

Query results

Reason: Because the when is not all possible values ​​of the case column, but an expression, but why does the result of 'male' appear, you need to think about it, and then update it after research and understanding

Correct spelling

select case sex when '1' then 'male' when '2' then 'female' else 'other' end as 'gender' from people;

Query results

"How to use mysql case when" is introduced here, thank you for reading.If you want to know more industry-related knowledge, you can pay attention to the Yisuyun website, and the editor will output more high-quality practical articles for you!