Introduction to the SQL CASE Statement

The SQL CASE statement in MySQL is a powerful tool for conditionally processing data within SQL queries. It allows you to perform different actions based on specified conditions, making it useful for transforming, categorizing, or aggregating data. In this guide, we'll explore the usage of the SQL CASE statement in MySQL.


Basic Syntax of the SQL CASE Statement

The basic syntax of the SQL CASE statement in a SELECT query is as follows:

            SELECT
                column1,
                column2,
                (CASE
                    WHEN condition1 THEN value1
                    WHEN condition2 THEN value2
                    ...
                    ELSE default_value
                END) AS alias
            FROM table_name;

You can specify multiple conditions and corresponding values, with an optional 

ELSE
clause for a default value.


Using the SQL CASE Statement in Queries

The SQL CASE statement can be used in various ways. Here are some common use cases:


1. Simple Conditional Transformation

You can use the SQL CASE statement to transform data based on a condition. For example:

            SELECT product_name, price,
                (CASE
                    WHEN price > 1000 THEN 'Expensive'
                    ELSE 'Affordable'
                END) AS price_category
            FROM products;

2. Categorizing Data

You can categorize data into specific groups using the SQL CASE statement. For instance:

            SELECT customer_name, purchase_amount,
                (CASE
                    WHEN purchase_amount >= 1000 THEN 'High Value'
                    WHEN purchase_amount >= 500 THEN 'Medium Value'
                    ELSE 'Low Value'
                END) AS customer_category
            FROM customers;

3. Aggregating Data

You can use the SQL CASE statement with aggregation functions to perform conditional aggregations. For example:

            SELECT department,
                SUM(CASE WHEN status = 'Completed' THEN 1 ELSE 0 END) AS completed_count,
                SUM(CASE WHEN status = 'Pending' THEN 1 ELSE 0 END) AS pending_count
            FROM tasks
            GROUP BY department;

Conclusion

The SQL CASE statement in MySQL is a versatile feature that allows you to perform conditional data processing in your SQL queries. By understanding its usage and applications, you can efficiently transform, categorize, and aggregate data to meet the specific needs of your database-driven applications.