When a UNION or UNION ALL query in PostgreSQL returns rows with unexpected NULL values in columns that clearly have data in the underlying tables, the cause is almost always a mismatch between the columns being combined — not a bug in PostgreSQL itself, which handles UNION very literally. The Problem You combine results from … Read more
Having an index on a column doesn’t guarantee PostgreSQL will actually use it, or that using it will make your query fast. When a query stays slow despite an index existing on the exact column being filtered or joined on, the planner usually has a good — if non-obvious — reason for its decision. The … Read more
The “too many connections” error in PostgreSQL means the server has hit its configured connection limit and is refusing new clients. It’s rarely caused by genuinely needing more simultaneous users than the default allows — far more often, it’s a sign that connections aren’t being closed properly somewhere in your application. The Problem New connection … Read more
A “connection refused” error between two containers on the same Docker network almost always means the PostgreSQL container isn’t reachable yet, isn’t listening where you expect, or the requesting container is looking in the wrong place entirely. Unlike a “connection refused” from a completely wrong host, this version is deceptively close to working, which makes … Read more
Resetting a PostgreSQL password inside a Docker container is a bit different from a normal installation, because you’re working through docker exec rather than a local shell, and the common instinct to just delete and recreate the container can wipe out your data if you’re not careful about volumes. The Problem You’ve lost or forgotten … Read more