逐步指南：如何确定符合特定条件的车辆？

确定符合条件的车辆：一个循序渐进的指南

简介

在某些情况下，我们可能需要确定一组车辆中符合特定条件的车辆。这可能涉及计算每个车辆的指标总和并筛选满足某些阈值的车辆。本文将提供一个逐步指南，演示如何使用 SQL 查询来确定符合条件的车辆。

步骤 1：计算每个车辆的指标总和

首先，我们需要计算每个车辆的指标总和。为此，我们可以使用 SUM() 聚合函数对每个车辆的每个指标进行求和。例如，以下 SQL 查询将计算每辆车的指标 1、2 和 3 的总和：

SELECT
  cars.variant,
  SUM(cars.metric_1) AS metric_1_total,
  SUM(cars.metric_2) AS metric_2_total,
  SUM(cars.metric_3) AS metric_3_total
FROM cars
GROUP BY cars.variant

步骤 2：筛选满足条件的车辆

计算出每个车辆的指标总和后，我们就可以筛选出满足特定条件的车辆。例如，要确定指标 1、2 和 3 总和均为 5 的车辆，我们可以使用以下查询：

SELECT
  cars.variant
FROM cars
HAVING
  metric_1_total = 5
  AND metric_2_total = 5
  AND metric_3_total = 5

步骤 3：将符合条件的车辆插入变量

确定符合条件的车辆后，我们可以将它们插入变量中以进行进一步处理。例如，要将符合条件的车辆的变体插入 @car1、@car2 和 @car3 变量中，我们可以使用以下查询：

SET @car1 = (
  SELECT variant
  FROM cars
  WHERE variant = (
    SELECT variant
    FROM (
      SELECT
        variant,
        SUM(metric_1) AS metric_1_total,
        SUM(metric_2) AS metric_2_total,
        SUM(metric_3) AS metric_3_total
      FROM cars
      GROUP BY variant
      HAVING
        metric_1_total = 5
        AND metric_2_total = 5
        AND metric_3_total = 5
    ) AS subquery
    ORDER BY metric_1_total DESC, metric_2_total DESC, metric_3_total DESC
    LIMIT 1
  )
);

SET @car2 = (
  SELECT variant
  FROM cars
  WHERE variant = (
    SELECT variant
    FROM (
      SELECT
        variant,
        SUM(metric_1) AS metric_1_total,
        SUM(metric_2) AS metric_2_total,
        SUM(metric_3) AS metric_3_total
      FROM cars
      GROUP BY variant
      HAVING
        metric_1_total = 5
        AND metric_2_total = 5
        AND metric_3_total = 5
    ) AS subquery
    ORDER BY metric_1_total DESC, metric_2_total DESC, metric_3_total DESC
    LIMIT 1 OFFSET 1
  )
);

SET @car3 = (
  SELECT variant
  FROM cars
  WHERE variant = (
    SELECT variant
    FROM (
      SELECT
        variant,
        SUM(metric_1) AS metric_1_total,
        SUM(metric_2) AS metric_2_total,
        SUM(metric_3) AS metric_3_total
      FROM cars
      GROUP BY variant
      HAVING
        metric_1_total = 5
        AND metric_2_total = 5
        AND metric_3_total = 5
    ) AS subquery
    ORDER BY metric_1_total DESC, metric_2_total DESC, metric_3_total DESC
    LIMIT 1 OFFSET 2
  )
);

示例

以下是一个示例，展示如何使用上述步骤来确定符合条件的车辆：

-- 计算每个车辆的指标总和
SELECT
  cars.variant,
  SUM(cars.metric_1) AS metric_1_total,
  SUM(cars.metric_2) AS metric_2_total,
  SUM(cars.metric_3) AS metric_3_total
FROM cars
GROUP BY cars.variant
HAVING
  metric_1_total = 5
  AND metric_2_total = 5
  AND metric_3_total = 5;

-- 将符合条件的车辆插入变量
SET @car1 = (
  SELECT variant
  FROM cars
  WHERE variant = (
    SELECT variant
    FROM (
      SELECT
        variant,
        SUM(metric_1) AS metric_1_total,
        SUM(metric_2) AS metric_2_total,
        SUM(metric_3) AS metric_3_total
      FROM cars
      GROUP BY variant
      HAVING
        metric_1_total = 5
        AND metric_2_total = 5
        AND metric_3_total = 5
    ) AS subquery
    ORDER BY metric_1_total DESC, metric_2_total DESC, metric_3_total DESC
    LIMIT 1
  )
);

SET @car2 = (
  SELECT variant
  FROM cars
  WHERE variant = (
    SELECT variant
    FROM (
      SELECT
        variant,
        SUM(metric_1) AS metric_1_total,
        SUM(metric_2) AS metric_2_total,
        SUM(metric_3) AS metric_3_total
      FROM cars
      GROUP BY variant
      HAVING
        metric_1_total = 5
        AND metric_2_total = 5
        AND metric_3_total = 5
    ) AS subquery
    ORDER BY metric_1_total DESC, metric_2_total DESC, metric_3_total DESC
    LIMIT 1 OFFSET 1
  )
);

SET @car3 = (
  SELECT variant
  FROM cars
  WHERE variant = (
    SELECT variant
    FROM (
      SELECT
        variant,
        SUM(metric_1) AS metric_1_total,
        SUM(metric_2) AS metric_2_total,
        SUM(metric_3) AS metric_3_total
      FROM cars
      GROUP BY variant
      HAVING
        metric_1_total = 5
        AND metric_2_total = 5
        AND metric_3_total = 5
    ) AS subquery
    ORDER BY metric_1_total DESC, metric_2_total DESC, metric_3_total DESC
    LIMIT 1 OFFSET 2
  )
);

-- 打印变量值
SELECT @car1, @car2, @car3;

该查询将输出以下结果：

SF90 Spider Q8 M2 Coupe

这表明变量 @car1、@car2 和 @car3 分别包含符合条件的车辆的变体：SF90 Spider、Q8 和 M2 Coupe。

常见问题解答

1. 我可以使用其他聚合函数吗？

是的，您可以使用其他聚合函数，如 AVG()（平均值）、MIN()（最小值）或 MAX()（最大值），具体取决于您的需求。

2. 我可以筛选多个条件吗？

是的，您可以使用 AND 和 OR 运算符来筛选多个条件。例如，要确定指标 1 大于 5 且指标 2 小于 10 的车辆，可以使用以下查询：

SELECT
  cars.variant
FROM cars
HAVING
  metric_1 > 5
  AND metric_2 < 10

3. 我可以对查询结果进行排序吗？

是的，您可以使用 ORDER BY 子句对查询结果进行排序。例如，要按指标 1 总和降序对符合条件的车辆进行排序，可以使用以下查询：

SELECT
  cars.variant
FROM cars
HAVING
  metric_1_total = 5
  AND metric_2_total = 5
  AND metric_3_total = 5
ORDER BY
  metric_1_total DESC

4. 我可以在不同的数据库中使用这些查询吗？

大多数数据库都支持 SUM() 聚合函数和 HAVING 子句，但语法可能略有不同。请查阅您使用的特定数据库的文档以获取更多信息。

5. 如何优化这些查询？

优化这些查询的方法有很多，包括使用索引、使用临时表以及优化子查询。有关如何优化 SQL 查询的更多信息，请参考相关资源。