PostgreSQL: Issues with JSONB Array Aggregation and Nested Queries
I'm working on a PostgreSQL 13 database where I need to aggregate JSONB data from multiple rows into a single JSON array. The challenge arises when I have a nested query that fails to return the expected results. My query is set up to retrieve user information along with their associated tags stored in a JSONB format. When I run the following query, I get unexpected results: ```sql SELECT u.id, u.name, (SELECT jsonb_agg(t.name) FROM tags t WHERE t.user_id = u.id) as tags FROM users u; ``` Instead of returning a JSON array of tag names for each user, I'm getting `null` for users with no tags, and for users with multiple tags, I only see one tag in the array. I tried using `COALESCE` to handle the `null` values, but that didn't resolve the issue: ```sql SELECT u.id, u.name, COALESCE((SELECT jsonb_agg(t.name) FROM tags t WHERE t.user_id = u.id), '[]'::jsonb) as tags FROM users u; ``` This still doesn't give the desired outcome. Moreover, when a user has multiple tags, they are not being aggregated properly. I suspect it might be due to how the subquery is structured or potentially the way the JSONB array is being constructed. Any advice on how to correctly aggregate the tags into a JSON array or if there's a more efficient way to achieve this would be greatly appreciated! Thanks in advance!