How would you optimise a slow query?
Model answer
Reproduce it, read the EXPLAIN plan, and find the costliest step. Typical fixes: add or adjust an index, select fewer columns and rows, rewrite subqueries or joins, avoid functions on indexed columns, update statistics, paginate with keysets, and cache or precompute heavy results. Measure after each change.
Learn this topic
Indexes and Faster Queries: EXPLAIN for Beginners in the course SQL for Beginners: Learn Databases Step by Step.
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