第一题： BEGIN; SELECT a.sku_name, a.category, a.qty FROM ( SELECT -- 这是一个只包含一个商品的总销量的表 sku_info.sku_name, category, sum( qty ) AS qty FROM sku_info, sales WHERE sku_info.sku_no = sales.sku_no GROUP BY sku_info.sku_no ) a WHERE 1 > ( -- 比这个销量大的商品熟练小于1，也就是效率最大的 SELECT count( DISTINCT a1.sku_name ) FROM ( SELECT -- 这是一个只包含一个商品的总销量的表 sku_info.sku_name, category, sum( qty ) AS qty FROM sku_info, sales WHERE sku_info.sku_no = sales.sku_no GROUP BY sku_info.sku_no ) a1 WHERE a1.category = a.category AND a1.qty > a.qty ) GROUP BY category; COMMIT;