PostgreSQL: Unexpected behavior with JOINs and missing rows on LEFT JOIN
I tried several approaches but none seem to work. I'm working with PostgreSQL 13 and I've run into an issue where a LEFT JOIN doesn't seem to return all the expected rows... I have two tables, `orders` and `customers`, where `orders` has a foreign key referencing `customers`. The `orders` table has a lot of entries, but not all of them have corresponding entries in the `customers` table. I expect the LEFT JOIN to return all orders, including those without a matching customer, but it seems to be omitting some rows. Here's the SQL query I've been using: ```sql SELECT o.id, o.order_date, c.name FROM orders o LEFT JOIN customers c ON o.customer_id = c.id; ``` When I execute this, I get a result set that includes some orders but skips others that should have NULL values for the customer name. However, when I run a simple COUNT, I see that the total number of orders in the database is what I expect. I tried adding a filtering condition to see if it was affecting the result: ```sql SELECT o.id, o.order_date, c.name FROM orders o LEFT JOIN customers c ON o.customer_id = c.id WHERE o.order_date > '2022-01-01'; ``` But that didn't change anything. I also tried checking for duplicate customer IDs in the `customers` table, and even ran: ```sql SELECT DISTINCT customer_id FROM orders WHERE customer_id NOT IN (SELECT id FROM customers); ``` Which returned IDs I expected to see in the LEFT JOIN result. I also verified that there are no triggers on the `orders` table that could be affecting the results. Is there a known limitation with LEFT JOINs that could cause this issue, or might I be missing something in my query or database design? Would appreciate any insights on how to troubleshoot this further. My development environment is Windows. Thanks in advance! I'm working on a application that needs to handle this. What am I doing wrong?