Use EXPLAIN to verify query plans

Use EXPLAIN to verify query plans | BeforeMerge Rules | BeforeMerge

Why this matters

EXPLAIN reveals the access path: whether an index is used, how many rows are examined, and whether a filesort or temporary table occurs. Checking it catches missing indexes and bad plans before they hit production.

-- Good: inspect the plan; watch type, key, rows, Extra
EXPLAIN SELECT * FROM orders WHERE customer_id = 42;
-- type=ref + key=idx_orders_customer_id is good;
-- type=ALL (full scan) signals a missing index.

Why This Matters

Related Rules

Catch this automatically on every PR

Why this matters