PostgreSQL: Handling Unexpected Duplicate Rows When Using DISTINCT with LEFT JOIN
I'm getting frustrated with I tried several approaches but none seem to work..... I'm stuck on something that should probably be simple. I'm encountering a perplexing situation where using `DISTINCT` in conjunction with a `LEFT JOIN` is returning unexpected duplicate rows in my PostgreSQL database (version 14). My goal is to retrieve unique records from the main table while including related data from the joined table without duplicates caused by multiple matching records in the joined table. Here’s the SQL query I’m currently using: ```sql SELECT DISTINCT a.id, a.name, b.detail FROM main_table a LEFT JOIN related_table b ON a.id = b.main_id; ``` However, I’ve noticed that when `related_table` has multiple rows for a single `main_table` entry, I end up getting duplicate rows in my result set for the `main_table`. For example, if `main_table` has one entry with ID 1 and `related_table` has two corresponding entries, my results include two rows with the same `id` and `name`, but different `detail` values. I’ve tried using `GROUP BY` as follows: ```sql SELECT a.id, a.name, array_agg(b.detail) FROM main_table a LEFT JOIN related_table b ON a.id = b.main_id GROUP BY a.id, a.name; ``` But this aggregates the `detail` values into an array instead of giving me unique rows. Is there a way to fetch unique records from `main_table` while still including the relevant data from `related_table` without facing the duplicates issue? I’m also considering whether there are any performance implications or best practices I should follow when dealing with multiple potential joins like this. Any insights or suggestions would be greatly appreciated! My development environment is macOS. Has anyone else encountered this? I'd really appreciate any guidance on this. My development environment is macOS. Am I missing something obvious? The stack includes Sql and several other technologies. I appreciate any insights! I'm working on a CLI tool that needs to handle this. Any pointers in the right direction?