Performing Conditional Aggregation for Dynamic Pivoting

SELECT
    product_id,
    SUM(CASE WHEN sale_month = 'Jan' THEN sale_amount ELSE 0 END) AS Sales_Jan,
    SUM(CASE WHEN sale_month = 'Feb' THEN sale_amount ELSE 0 END) AS Sales_Feb,
    SUM(CASE WHEN sale_month = 'Mar' THEN sale_amount ELSE 0 END) AS Sales_Mar,
    SUM(sale_amount) AS Total_Sales -- Optional: Total sales across all selected months
FROM (
    -- Subquery to extract month or other relevant grouping column
    SELECT
        product_id,
        DATE_FORMAT(sale_date, '%b') AS sale_month, -- For MySQL. Use TO_CHAR(sale_date, 'Mon') for PostgreSQL, FORMAT(sale_date, 'MMM') for SQL Server
        amount AS sale_amount
    FROM sales
    WHERE sale_date >= '2023-01-01' AND sale_date < '2023-04-01'
) AS MonthlySales
GROUP BY product_id
ORDER BY product_id;

-- Example 'sales' table structure:
-- CREATE TABLE sales (
--     sale_id INT PRIMARY KEY AUTO_INCREMENT,
--     product_id INT,
--     sale_date DATE,
--     amount DECIMAL(10, 2)
-- );
-- INSERT INTO sales (product_id, sale_date, amount) VALUES
-- (101, '2023-01-05', 100.00),
-- (102, '2023-01-15', 250.50),
-- (101, '2023-02-10', 120.00),
-- (103, '2023-02-20', 300.00),
-- (102, '2023-03-01', 180.00),
-- (101, '2023-03-25', 90.00);