What does case when mean in sql

<blockquote><p>The CASE WHEN statement is a conditional statement used to evaluate multiple expressions and return different values ​​based on conditions. It evaluates the conditions from top to bottom, returning the value corresponding to the first true condition, or the optional default value if there is no true condition. </p></blockquote> <p><img src="/static/imghw/default1.png" data-src="https://img.php.cn/upload/article/202404/28/2024042809391573136.jpg" class="lazy" alt="What does case when mean in sql" ></p> <p><strong>CASE WHEN statement </strong></p> <p><strong>Definition: </strong></p> <p> in SQL The CASE WHEN statement is a conditional statement used to evaluate multiple expressions based on a given conditional comparison. It allows us to return different values ​​based on different situations. </p> <p><strong> Grammar: </strong></p><div class="code" style="position:relative; padding:0px; margin:0px;"><pre class='brush:php;toolbar:false;'>CASE WHEN condition1 THEN result1 WHEN condition2 THEN result2 ... ELSE default_result END</pre><div class="contentsignin">Copy after login</div></div><p><strong> Usage: </strong></p><ul><li>##condition1<code>, </code>condition2 <code>, ...: Conditions to be evaluated. </code></li><li>result1<code>, </code>result2<code>, ...: The value to be returned if the corresponding condition is true. </code></li><li>default_result<code>: The optional default value to return if all conditions are false. </code></li></ul><p>How it works: <strong></strong></p>The CASE WHEN statement evaluates conditions from top to bottom until it finds the first condition that is true. If a true condition is found, the corresponding <p>result<code> value is returned. If there is no true condition, returns the </code>default_result<code> value if specified. </code></p><p>Example:<strong></strong></p>Get student grade level:<p><div class="code" style="position:relative; padding:0px; margin:0px;"><pre class='brush:php;toolbar:false;'>CASE WHEN grade >= 90 THEN 'A' WHEN grade >= 80 THEN 'B' WHEN grade >= 70 THEN 'C' WHEN grade >= 60 THEN 'D' ELSE 'F' END</pre><div class="contentsignin">Copy after login</div></div><p>Advantages:<strong></strong></p>##Simplify Conditional logic, avoid using nested IF-ELSE statements. <ul> <li>Improve code readability and maintainability. </li> <li> </ul>Note: <p><strong></strong></p>CASE WHEN statement can contain multiple branches. <ul> <li>default_result<li> is optional, if not specified the result will be NULL. <code></code>Comparison conditions use comparison operators such as </li>=<li>, <code>></code>, <code><</code>. <code></code> </li> </ul>

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