This article explains the concepts of cardinality and HINT in MySQL, demonstrates how inaccurate cardinality can lead to sub‑optimal execution plans, and shows how applying index_merge hints dramatically reduces query cost and row scans for multi‑column predicates.
A SAP month‑end CO module query suffered severe slowdown despite standard index hints, prompting a deep dive into execution plans, statistics, and a little‑known num_index_keys hint that dramatically improves IN‑list iterator access and reduces filter overhead.
This article explains why a SQL Server paging query using TOP can take minutes, demonstrates how switching to ROW_NUMBER() with CTEs, index hints, temporary tables, and hash joins dramatically reduces execution time, and provides practical tips for handling large page numbers.
This article walks through a real Oracle OLTP query that took 28 seconds per execution, explains how execution‑plan analysis, index hints, and correcting stale statistics reduced the runtime to sub‑millisecond levels, and shows the final combined index that eliminated the performance issue.
