MySQL 5.7: implementing Group By Returning Unexpected Aggregated Results Across Different Columns
Quick question that's been bugging me - I'm working through a tutorial and I'm working on a personal project and I'm working with a puzzling scenario with MySQL 5.7 when using a `GROUP BY` clause that seems to return unexpected results when aggregating across multiple columns... My query is meant to summarize sales data by product category and month, but the results are not aligning as anticipated. Here's the SQL I'm using: ```sql SELECT category, MONTH(sale_date) AS sale_month, SUM(amount) AS total_sales FROM sales GROUP BY category, sale_month; ``` The `sales` table contains the following columns: - `id` (INT) - `category` (VARCHAR) - `sale_date` (DATETIME) - `amount` (DECIMAL) However, the results show duplicate rows for some categories, and the `total_sales` figures seem to be inflated. For instance, a single category is returning multiple rows for the same month with different total sales values. I’ve verified that there are no duplicate records in the `sales` table, yet the aggregated output seems inconsistent. I’ve tried using `DISTINCT` on the `category` and `sale_month` within the `SUM` function: ```sql SELECT category, MONTH(sale_date) AS sale_month, SUM(DISTINCT amount) AS total_sales FROM sales GROUP BY category, sale_month; ``` However, this change didn’t resolve the scenario either. Additionally, I experimented with including `sale_date` in the `GROUP BY` clause: ```sql SELECT category, sale_date, SUM(amount) AS total_sales FROM sales GROUP BY category, sale_date; ``` But this just added more rows instead of addressing the duplication. I suspect it might have something to do with how MySQL handles query execution and groupings, but I need to pinpoint the exact cause. Has anyone encountered similar issues or can offer insights on best practices with grouping and aggregating in MySQL? Any guidance would be greatly appreciated! Has anyone else encountered this? What's the correct way to implement this? This is part of a larger application I'm building.