Question

查询1

SELECT m.Name, p.Name, p.Price
    FROM Manufacturers m INNER JOIN Products p
        ON m.Code = p.Manufacturer
WHERE p.Price IN (SELECT MAX(pp.Price) FROM Products pp GROUP BY pp.Manufacturer);

查询2

  select m.Name as ManufName, p.Name as ProductName, p.Price as ProductPrice
    from Manufacturers m inner join Products p
      on m.Code = p.Manufacturer
        where p.Price =   (select max(sub_p.Price)
                                  from Products sub_p
                                    where m.Code = sub_p.Manufacturer);

哪一个应该花费更少的时间？

Answer 1

这取决于。表格，索引等的大小尝试它们并进行比较。

但是，对数据库一无所知，我会猜测查询1应该表现得更好。查询2有correlated sub query，这将使优化器使用嵌套循环。

这两个查询中的哪一个更有效或运行最佳？

1 个答案: