How to use when in mysql

The WHEN clause in MySQL is used to specify the actions to be performed when specific conditions are met. It supports: Single condition check, for example: CASE WHEN salary >= 10000 THEN 'High'. Multiple condition processing, for example: CASE WHEN age < 18 THEN 'Child' WHEN age < 65 THEN 'Adult'. Default result, for example: CASE WHEN gender = 'M' THEN 'Male' ELSE 'Female'. The WHEN clause provides concise syntax, multi-condition processing, and default results.

WHEN usage in MySQL

Overview:
The WHEN clause is CASE A branch in an expression that specifies an action to perform when a specific condition is met.

Syntax:

<code class="sql">CASE expression
    WHEN value1 THEN result1
    WHEN value2 THEN result2
    ...
    ELSE default_result
END</code>

Usage:

1. ##Single condition:

   • The WHEN clause can specify a single condition, and if the condition is true, the corresponding result is returned.

     For example:
     

     <code class="sql">CASE WHEN salary >= 10000 THEN 'High'
     ELSE 'Low'
     END</p>
     <li>
     <p>Multiple conditions: <strong></strong></p>
     <ul><li>There can also be multiple A WHEN clause is used to handle different conditions. <p>For example: <br></p>
     <pre class="brush:php;toolbar:false"><code class="sql">CASE WHEN age < 18 THEN 'Child'
     WHEN age < 65 THEN 'Adult'
     ELSE 'Senior'
     END</code>

2. Default result:

   • The ELSE clause specifies when The default result when all conditions of the WHEN clause are not met.

     For example:
     

     <code class="sql">CASE WHEN gender = 'M' THEN 'Male'
     ELSE 'Female'
     END</code>

Advantages:

Concise: CASE expression is easier to use than IF -ELSE statements are more concise and readable.
• Multi-condition processing: Situations with multiple conditions can be easily handled.
• Default results: Provides default values ​​for handling all situations.

Limitations:

Performance: CASE expressions may be slower than IF-ELSE statements for complex or large amounts of data.

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