php - MySQL 统计查询优化

Question

我正在尝试稍微优化我的查询，但不能完全正确。

我希望从表格中获取一些统计信息

我要查询主要贡献者

SELECT `name`, `amount` FROM `customers` ORDER by `amount` DESC LIMIT 10

但我也想获得所有记录中金额的 SUM 和 AVG，而不仅仅是前 10 名。我不确定如何在没有新查询的情况下执行此操作。

Answer 1

尝试

SELECT `name`, `amount`, sa.sum_a, sa.avg_a
FROM `customers`, (select sum(amount) as sum_a, avg(amount) as avg_a from customers) sa
ORDER by `amount` DESC 
LIMIT 10

Answer 2

如果您想要前 10 个用户以及表中所有SUM行的和，您可以制作和的笛卡尔积，如下所示：AVGSUMAVG

SELECT 
    a.name, a.amount, b.amtsum, b.amtavg
FROM customers a
CROSS JOIN (SELECT SUM(amount) AS amtsum, AVG(amount) AS amtavg FROM customers) b
ORDER BY amount DESC
LIMIT 10

请记住， 和 的值SUM将AVG在返回的所有 10 行上重复——它们将是相同的。

如果您想要每个用户的金额总和和平均值，您可以执行以下操作：

SELECT a.name, a.amount, b.amtsum, b.amtavg
FROM customers a
INNER JOIN
(
    SELECT name, SUM(amount) AS amtsum, AVG(amount) AS amtavg
    FROM customers
    GROUP BY name
) b ON a.name = b.name
ORDER BY a.amount DESC
LIMIT 10

Answer 3

一种选择是使用子查询

SELECT 
    `name`, `amount`,
    (SELECT SUM(amount) FROM customers) as summation,
    (SELECT AVG(amount) FROM customers) as average
 FROM 
    `customers` ORDER by `amount` DESC LIMIT 10 

Answer 4

在这种情况下，最干净且通常也是最快的方法是两个查询。获取相同的聚合十次没有任何优势。

确保您在amount. 这将为您节省每个查询对表的完整排序。

Answer 5

您可以使用 MySQLExplain关键字进行查询优化。

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