9 articles tagged #Database Optimization
Are your SQL CTE and subquery versions returning different row counts? Learn why this happens, how query logic, joins, filtering, and execution plans affect results, and how to debug row count discrepancies across major SQL databases.
You ran the same query twice — once with DISTINCT and once with GROUP BY — and got different row counts. This guide breaks down exactly why that happens and how to get the result you actually want.
You created a GIN index on a JSONB column but EXPLAIN ANALYZE still shows a sequential scan. Here's why PostgreSQL ignores your index and the exact steps to fix it without rewriting your schema.
Your LATERAL JOIN looks correct, but it returns no rows — even though the outer table has data and the subquery runs fine in isolation. Here's why it silently fails and how to fix it.
Bulk inserts combined with PostgreSQL's ON CONFLICT DO NOTHING can dramatically improve performance and simplify deduplication. However, many developers are surprised when rows silently disappear during large imports. Learn why missing rows occur, how SQLAlchemy handles conflicts, and how to safely
N+1 query bugs in Django serializers can silently turn a fast endpoint into a database-hammering bottleneck. Learn how to detect them with django-debug-toolbar and nplusone, then fix them permanently with select_related and prefetch_related.
PostgreSQL 12 changed how CTEs are handled, and the difference between materialized and inlined CTEs can silently kill your query performance. Here's how to diagnose the problem and fix it with one keyword.
You added an index, ran your query, and EXPLAIN ANALYZE still shows a sequential scan. Before you blame PostgreSQL, there are at least six specific reasons this happens — and each one has a clear fix.
Your INSERT ... ON CONFLICT DO UPDATE looks right, but rows are never actually updated. This guide digs into the common causes — wrong conflict targets, excluded column mistakes, and WHERE clause gotchas — and shows you how to fix each one.