Question

以下查询需要花费太多时间（目前为0.8169秒）来显示20个条目，我无法找到原因......

SELECT
        `Order`.ID,
        Order_Type.Description as OrderTypeDescription,
        `Order`.OrderType as OrderType,
        DATE_FORMAT(`Order`.InsertDate, '%d.%m.%Y') as OrderInsertDate,
        round(sum(Item_Price.Amount),2) as OrderAmount,
        c1.ID as buyerCustomerId,
        c2.ID as sellerCustomerId,
        c1.CompanyName as BuyerCompany,
        c2.CompanyName as SellerCompany,
        c1.ID as BuyerCustomer,
        c2.ID as SellerCustomer
    FROM `Order`
        INNER JOIN Order_Type ON Order_Type.ID=`Order`.OrderType
        INNER JOIN Customer as c1 ON c1.ID=`Order`.BuyerCustomer
        INNER JOIN Customer as c2 ON c2.ID=`Order`.SellerCustomer
        INNER JOIN Item ON Item.`Order`=`Order`.ID
        INNER JOIN Item_Price ON Item_Price.Item=Item.ID
    GROUP BY `Order`.ID,OrderType,OrderTypeDescription,buyerCustomerId,sellerCustomerId,BuyerCustomer,SellerCustomer
    ORDER BY `Order`.ID DESC
    LIMIT 20

EXPLAIN显示以下输出：http://pastebin.com/5f9QYizq

我在优化查询方面并不是很擅长，但我认为性能不佳的原因可能是项目和item_price表的连接（和总和），因为两个表中都有很多行（项目）：16974，item_price：23981）因为每个项目都有一个或多个item_prices，总计订单金额。

如何更快地进行此查询？

Answer 1

您可以尝试使用相关子查询而不是public class UnorderedEnumerableComparer<T> : IEqualityComparer<IEnumerable<T>> { public bool Equals(IEnumerable<T> x, IEnumerable<T> y) { return x.OrderBy(i => i).SequenceEqual(y.OrderBy(i => i)); } // Just the count of the array, // it violates the rule of hash code but should be fine here public int GetHashCode(IEnumerable<T> obj) { return obj.Count(); } }：

group by

这应节省SELECT o.ID, ot.Description as OrderTypeDescription, ot.OrderType as OrderType, DATE_FORMAT(o.InsertDate, '%d.%m.%Y') as OrderInsertDate, (SELECT round(sum(ip.Amount), 2) FROM Item i INNER JOIN Item_Price ip ON ip.Item = i.ID WHERE i.`Order` = o.ID ) as OrderAmount, c1.ID as buyerCustomerId, c2.ID as sellerCustomerId, c1.CompanyName as BuyerCompany, c2.CompanyName as SellerCompany, c1.ID as BuyerCustomer, c2.ID as SellerCustomer FROM `Order` o INNER JOIN Order_Type ot ON ot.ID = o.OrderType INNER JOIN Customer c1 ON c1.ID = o.BuyerCustomer INNER JOIN Customer c2 ON c2.ID = `Order`.SellerCustomer ORDER BY o.ID DESC LIMIT 20;开销。

您甚至可以将GROUP BY移动到子查询，假设连接没有过滤任何行：

LIMIT

MySQL Query非常慢

1 个答案: