How to debug a slow SQL query
A careful workflow from the symptom to evidence, a testable hypothesis and verification.
TuningLens knowledge base
SQL tuning guides
Direct answers for developers investigating MySQL and MariaDB SELECT queries. Each guide states its version scope, cites primary documentation and treats every recommendation as a hypothesis to verify.
Start with the question you have
How to read a MySQL EXPLAIN plan
Read access paths, indexes, row estimates, joins and Extra without overclaiming what a plan proves.
Is MySQL EXPLAIN ANALYZE safe?
Understand that it executes the statement and plan a safer diagnostic run.
MySQL composite index column order
Reason about leftmost prefixes, equality, ranges, ordering and verification.
What Using filesort means in MySQL
Learn when a filesort matters and how to test an ordering-index hypothesis.
MariaDB ANALYZE statement
Use actual execution statistics with the right safety and version caveats.
Worked examples
See how the process applies to an order-history query and a deep-pagination query. These examples are illustrative and make no measured speedup claims.