Query Optimization。EXPLAIN ANALYZE+BUFFERS+JSON Format・Cost-Based Optimizer CBO・Statistics+Histograms・B-Tree Index (PG/MySQL Default)・Hash Index・GIN Generalized Inverted (PG・JSONB/Array/Full-text)・GIST Generalized Search Tree (PG・Geometric)・BRIN Block Range Index (PG・大表)・Partial Index・Expression Index・Covering Index INCLUDE・Multicolumn Index・Index-Only Scan・Bitmap Heap Scan・Plan Hint (pg_hint_plan)、2026年pg_stat_statements+auto_explain主流化。