PostgreSQL: Unexpected results when using LEFT JOIN with NULLs in WHERE clause for filtered aggregation
I'm dealing with I'm working on a project and hit a roadblock..... I've looked through the documentation and I'm still confused about I've run into an scenario with a PostgreSQL 13 query that involves a LEFT JOIN and a filtering condition in the WHERE clause... The query is intended to aggregate data from two tables, but I'm getting unexpected results when there are NULL values in the joined table. Here's the query I'm using: ```sql SELECT a.id, COUNT(b.id) AS related_count FROM table_a a LEFT JOIN table_b b ON a.id = b.a_id WHERE b.status = 'active' GROUP BY a.id; ``` I expect to see counts of related records for each record in `table_a`, even if there are no matching records in `table_b`. However, when there are NULLs from the LEFT JOIN, the records from `table_a` are not included in the results at all. I also tried moving the filtering condition to the JOIN clause like this: ```sql SELECT a.id, COUNT(b.id) AS related_count FROM table_a a LEFT JOIN table_b b ON a.id = b.a_id AND b.status = 'active' GROUP BY a.id; ``` This change did provide some results, but the count for `related_count` is still off. It seems to be counting only the active records and not considering the records from `table_a` that have no matches in `table_b`. Can someone explain why this is happening and how to modify the query to get the expected behavior? I want to include all records from `table_a` while counting only the active related records from `table_b`. Any insights or best practices for dealing with this type of aggregation in SQL would be appreciated! What am I doing wrong? For context: I'm using Sql on Ubuntu. Any help would be greatly appreciated! I'm using Sql stable in this project. What am I doing wrong?