Leftmost Prefix

Selected Java Interview Questions

Jan 19, 2025 · Databases

Understanding MySQL Covering Indexes, Table Lookups, and the Leftmost Prefix Rule

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.

Back TableCovering IndexDatabase Optimization

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Understanding MySQL Covering Indexes, Table Lookups, and the Leftmost Prefix Rule

Selected Java Interview Questions

Nov 24, 2022 · Databases

Common MySQL Index Failure Scenarios and Optimization Techniques

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.

DatabaseIndexLeftmost Prefix

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Common MySQL Index Failure Scenarios and Optimization Techniques