PostgreSQL: Unexpected NULL Values in JOIN with COALESCE Function
I'm trying to implement Hey everyone, I'm running into an issue that's driving me crazy... I'm facing an issue in my PostgreSQL 13 database where I am getting unexpected NULL values when performing a JOIN between two tables while using the COALESCE function. I have two tables, `orders` and `customers`, where `orders` has a foreign key `customer_id` referencing `customers`. My goal is to retrieve all orders along with the customer names, and if a customer name is NULL, I want to replace it with 'Unknown'. However, the result set still shows NULLs for some customer names. Here’s the query I’m using: ```sql SELECT o.order_id, COALESCE(c.name, 'Unknown') AS customer_name FROM orders o LEFT JOIN customers c ON o.customer_id = c.id; ``` I expected that all orders would be returned with either the customer name or 'Unknown', but some rows still show NULL for `customer_name`. I've double-checked the `customer_id` values in the `orders` table, and they seem to match the existing IDs in the `customers` table. Additionally, I ran the following query to see the distinct `customer_id` values from the `orders` table and noticed that one of the IDs does not exist in the `customers` table: ```sql SELECT DISTINCT customer_id FROM orders; ``` Could it be that the NULL values are appearing because of the missing customer records? Is there a better way to handle this situation or to ensure that I don't get NULLs in my final output? Any insights would be appreciated! Thanks, I really appreciate it! This is happening in both development and production on Debian. Hoping someone can shed some light on this.