This article details seven common MySQL index failure scenarios—including leftmost prefix violations, function usage on indexed columns, implicit type conversion, leading wildcards in LIKE, OR with non-indexed columns, IS NOT NULL, and NOT IN/EXISTS—with concrete SQL examples showing both failing and optimized queries.
This article explains what MySQL composite (multi‑column) indexes are, how they are built and ordered, the leftmost‑prefix rule that governs their usage, factors such as cardinality and selectivity for optimal design, and common scenarios where the index may become ineffective.
This article explains MySQL covering indexes, how table lookups (back‑table operations) work, and the leftmost prefix rule for composite indexes, providing practical examples and tips for optimizing query performance in interview scenarios.
This article explains key MySQL interview topics—including covering indexes that let queries avoid table lookups, the back‑table process when secondary indexes lack needed columns, and the leftmost prefix rule for composite indexes—providing clear examples and optimization tips.
This article explains MySQL’s leftmost prefix principle, shows how composite indexes are built and used, demonstrates which query patterns trigger index usage or full‑table scans, and provides practical tips for SELECT *, functions, LIKE, OR, IN, ORDER BY and sub‑queries to avoid index loss.
This article explains why many MySQL queries cause index inefficiency, details the leftmost prefix rule for composite indexes, illustrates common index‑breaking patterns such as SELECT *, functions, range queries, LIKE, OR, IN, ORDER BY, and introduces Index Condition Pushdown (ICP) as an optimization to reduce row lookups.
