SQL queries, joins, keys and database concepts
Learn PHP PDO — connecting to MySQL, fetching rows, and preventing SQL injection with prepared statements.
Learn tsvector, tsquery, GIN indexes, ranking, and multi-language search.
Learn EXPLAIN FORMAT=JSON, EXPLAIN ANALYZE, and identifying bottlenecks.
Learn aggregate functions, GROUP BY to group results, and HAVING to filter groups.
Learn JSONB operators, GIN indexes, jsonb_set, and performance patterns.
Learn B-Tree, hash, composite, and covering indexes — when each type helps.