EXPLAIN FORMAT=TREE
SELECT o.id
FROM orders o
JOIN users u ON u.id = o.user_id
WHERE u.city = 'shanghai'
ORDER BY o.created_at DESC
LIMIT 10;

-- 输出形如：
-- -> Limit: 10 row(s)
--     -> Sort: o.created_at DESC, limit input to 10 row(s) per chunk
--         -> Stream results
--             -> Nested loop inner join

EXPLAIN FORMAT=JSON
SELECT * FROM orders WHERE user_id = 100;
-- JSON 中含 cost_info、key_length、used_key_parts 等字段，便于脚本解析