Telling apart 3 reasons MySQL isn't using your index

<p>You are reading the slow query log in CloudWatch Logs or a similar tool, and one query has a <code>Rows_examined</code> (rows read) about equal to the table's row count, or larger, while its <code>Rows_sent</code> (rows returned) is only a few. <code>SHOW INDEX</code> shows an index on the column used in the condition. Running EXPLAIN on the same query in a staging environment restored from a b

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