Query optimization

Remove WordPress database bloat including orphaned postmeta rows, unlimited post revisions, expired transients, and spam comments with safe SQL queries and WP-CLI commands.

Understand how MySQL indexes work and learn to add the right indexes to WordPress custom tables and meta queries to eliminate slow full-table scans.

Create MySQL views to encapsulate complex WordPress JOIN queries into reusable virtual tables you can query from PHP with wpdb.

Use MySQL IN, NOT EXISTS and derived table subqueries to filter and clean WordPress database records efficiently.

Learn INNER JOIN, LEFT JOIN and multi-table joins with practical WordPress SQL examples for posts, meta and taxonomy tables.

Use MySQL GROUP BY, ORDER BY, HAVING and aggregate functions to count and summarise WordPress database records.

Learn how to read MySQL EXPLAIN output to identify missing indexes and eliminate full-table scans.

Find and fix oversized autoloaded options Every WordPress request starts by loading all options marked as autoload = 'yes' in one query. They are kept in memory (in the object cache under the key alloptions), so later get_option() calls for them cost nothing. The problem is that plugins create options with autoload on by default,…

Make secondary WP_Query loops cheaper: no_found_rows, cache flags and fields A default new WP_Query() does more than select posts. It also counts all matching posts for pagination (SQL_CALC_FOUND_ROWS plus SELECT FOUND_ROWS()), loads the meta of all found posts into the cache and loads their terms. For the main query of an archive that is what…