Multiple Case When SQL

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How can I use multiple CASE WHEN statements in SQL to handle different conditions and return different results?

Multiple CASE WHEN statements in SQL allow you to define a series of conditions and corresponding results. This is useful for implementing complex logic and returning different values based on various criteria. It's a powerful tool for data transformation and filtering.

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Description

The CASE statement in SQL is a powerful conditional expression. It allows you to evaluate different conditions and return different results based on those conditions. A single CASE statement can handle multiple conditions, making it a versatile tool for data manipulation. This is particularly useful when you need to apply different logic based on various criteria. For instance, you might need to categorize customer orders based on their value, or assign different discounts based on product type. Multiple CASE WHEN statements are used to handle these scenarios. Each WHEN clause checks a condition, and if it's true, the corresponding THEN clause is executed. If none of the WHEN clauses are true, the ELSE clause (if present) is executed. This structured approach makes your SQL code more readable and maintainable, especially when dealing with complex decision-making logic.

Why Multiple Case When SQL is important

Multiple CASE WHEN statements are crucial for creating flexible and adaptable SQL queries. They enable complex data transformations and calculations based on various conditions, making them essential for data analysis and reporting. This structured approach improves code readability and maintainability, especially in large and complex database applications.

Example Usage


CREATE TABLE Customers (
    CustomerID INT PRIMARY KEY,
    CustomerName VARCHAR(50),
    OrderValue DECIMAL(10, 2)
);

INSERT INTO Customers (CustomerID, CustomerName, OrderValue)
VALUES
(1, 'Alice', 100.00),
(2, 'Bob', 250.00),
(3, 'Charlie', 50.00),
(4, 'David', 1000.00);

SELECT
    CustomerID,
    CustomerName,
    OrderValue,
    CASE
        WHEN OrderValue < 100 THEN 'Low Value'
        WHEN OrderValue BETWEEN 100 AND 500 THEN 'Medium Value'
        WHEN OrderValue > 500 THEN 'High Value'
        ELSE 'Unknown'
    END AS OrderCategory
FROM
    Customers;

Common Mistakes

Forgetting the END keyword after the last WHEN or ELSE clause.
Using incorrect data types in the WHEN clause (e.g., comparing strings to numbers without explicit type conversion).
Not considering all possible cases, leading to incomplete or incorrect results.
Using nested CASE statements without proper indentation, making the code hard to read and debug.

Multiple Case When SQL

How can I use multiple CASE WHEN statements in SQL to handle different conditions and return different results?

Description

Why Multiple Case When SQL is important

Example Usage

Common Mistakes

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