What does case mean in sql

The CASE statement is a SQL control flow statement that performs different actions based on specific conditions. The syntax is: CASE WHEN THEN WHEN THEN ... ELSE END. It selects different blocks of code by checking a given expression and assigns grades, sets flags and performs complex queries as needed. CASE statements include simple CASE statements, search CASE statements and values ​​CA

CASE statement in SQL

What is a CASE statement?

The CASE statement is a SQL control flow statement used to perform different operations based on specific conditions. It allows you to select different blocks of code based on the value of a certain expression.

Syntax of the CASE statement

<code class="sql">CASE
    WHEN <expression1> THEN <result1>
    WHEN <expression2> THEN <result2>
    ...
    ELSE <default_result>
END</code>

How the CASE statement works

The CASE statement evaluates the given expression and presses WHEN clauses are checked sequentially. If a WHEN clause expression is true, the corresponding RESULT clause is executed. If all WHEN clause expressions are false, the ELSE clause, if present, is executed.

When to use the CASE statement

The CASE statement is usually used in the following situations:

• Select different column values ​​based on conditions
• Set different flags based on different value ranges
• Perform complex conditional queries

Example

The following is an example using CASE Example of a statement that assigns grades based on a score range:

<code class="sql">SELECT
    CASE
        WHEN score >= 90 THEN 'A'
        WHEN score >= 80 THEN 'B'
        WHEN score >= 70 THEN 'C'
        ELSE 'F'
    END AS grade
FROM students;</code>

Other Types

In addition to the syntax above, there are other types of CASE statements, including:

• Simple CASE statement: There is only one CASE keyword and one THEN clause.
• Search for CASE statements: Use the WHEN THEN clause sequence to search for specific values.
• Value CASE statement: Use a sequence of VALUE WHEN clauses to match column values.

By using different types, you can tailor the behavior of the CASE statement to your needs.

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