customer_id にだけインデックスがある orders で、次の EXPLAIN ANALYZE の出力が得られた。改善策として適切なものはどれか。 ``` Bitmap Heap Scan on orders (actual time=3.293..6.041 rows=17 loops=1) Recheck Cond: ((customer_id >= 1) AND (customer_id <= 30000)) Filter: (status = 'pending'::text) Rows Removed by Filter: 59983 Heap Blocks: exact=386 -> Bitmap Index Scan on idx_orders_customer (actual time=3.086..3.087 rows=60000 loops=1) Index Cond: ((customer_id >= 1) AND (customer_id <= 30000)) ```