MySQL 8.0 - Query Returning Incorrect Row Count When Using UNION with GROUP BY
I'm getting frustrated with I'm maintaining legacy code that Hey everyone, I'm running into an issue that's driving me crazy... I'm working on a personal project and I'm working with an scenario where a query that uses `UNION` along with `GROUP BY` returns an unexpected row count. My intention is to combine two result sets, each aggregated by a specific column, but the results don't seem to align with my expectations. Here's a simplified version of my query: ```sql SELECT department, COUNT(*) as employee_count FROM employees WHERE status = 'active' GROUP BY department UNION SELECT department, COUNT(*) as employee_count FROM contractors WHERE status = 'active' GROUP BY department; ``` When I run this, I expect to see a combined list of active employees and contractors by department, but the final output seems to have duplicates, resulting in a total count that's higher than anticipated. I've tried using `UNION ALL`, but that just adds to the total count without removing duplicates. Additionally, I’ve verified that there are no duplicate entries in either the `employees` or `contractors` tables. Could the question be arising from how `UNION` handles the groups? I also tried wrapping the entire union in a subquery and performing a second `GROUP BY` to consolidate the counts, but that didn’t yield the correct results either. Here’s what I attempted: ```sql SELECT department, SUM(employee_count) as total_count FROM ( SELECT department, COUNT(*) as employee_count FROM employees WHERE status = 'active' GROUP BY department UNION ALL SELECT department, COUNT(*) as employee_count FROM contractors WHERE status = 'active' GROUP BY department ) as combined GROUP BY department; ``` However, the `total_count` is still not matching what I believe it should be based on the underlying data. I'm working with MySQL version 8.0.26. Any insights on why this might be happening, or how to properly structure this query to get an accurate row count? This is part of a larger application I'm building. Thanks in advance! This is for a CLI tool running on Ubuntu 20.04. Any examples would be super helpful. I'm working in a Ubuntu 20.04 environment. Any feedback is welcome! The project is a REST API built with Sql. I'm open to any suggestions. My team is using Sql for this microservice. Is there a better approach?