MySQL: Difficulty retrieving unique records from two joined tables with filtering on NULL values
I've searched everywhere and can't find a clear answer... I'm facing an issue in MySQL 8.0 where I need to retrieve unique records from two joined tables, but my query doesn't seem to filter out duplicates correctly, especially when dealing with NULL values in one of the tables. I have two tables, `orders` and `customers`, and I want to get a list of unique customers who have placed orders, but only if their `last_order_date` is not NULL. Here's what my query looks like: ```sql SELECT DISTINCT c.customer_id, c.name FROM customers c JOIN orders o ON c.customer_id = o.customer_id WHERE o.last_order_date IS NOT NULL; ``` However, I'm still getting duplicate customer entries in the results. I even tried using `GROUP BY` but ran into the same issue. Here’s the altered query I attempted: ```sql SELECT c.customer_id, c.name, COUNT(o.order_id) AS order_count FROM customers c JOIN orders o ON c.customer_id = o.customer_id WHERE o.last_order_date IS NOT NULL GROUP BY c.customer_id, c.name; ``` Instead of unique customer records, I'm seeing customers listed multiple times based on how many orders they have made. I suspect it might have something to do with how the JOIN is structured or the way I'm counting the orders. The `last_order_date` is a DATETIME field, and I want to make sure I only get those customers who have actually placed orders. Any insights into how I can properly filter the results to ensure each customer is unique, while still meeting the required conditions on the `last_order_date`? I've also checked for subtle data issues, but everything seems normal on that front. Thanks for your help! I recently upgraded to Sql latest. Any ideas how to fix this?