MySQL GROUP BY 年龄范围，包括空范围答案

【问题标题】：MySQL GROUP BY age range including null rangesMySQL GROUP BY 年龄范围，包括空范围
【发布时间】：2010-07-14 15:17:01
【问题描述】：

我正在尝试按年龄段计算人数，我几乎可以解决 2 个问题：

如果给定年龄范围内没有人 (NULL)，则该年龄范围不会出现在结果中。例如，在我的数据中没有“Over 80”的条目，因此不会出现日期范围。基本上，当缺少日期范围时，这看起来像是编程错误。
我想以特定方式对结果进行排序。在下面的查询中，因为 ORDER BY 是按年龄范围排列的，所以“20 - 29”的结果排在“20 岁以下”的结果之前。

这是 db 表“查询”的示例：

inquiry_id  birth_date
1           1960-02-01
2           1962-03-04
3           1970-03-08
4           1980-03-02
5           1990-02-08

这是查询：

SELECT
    CASE
        WHEN age < 20 THEN 'Under 20'
        WHEN age BETWEEN 20 and 29 THEN '20 - 29'
        WHEN age BETWEEN 30 and 39 THEN '30 - 39'
        WHEN age BETWEEN 40 and 49 THEN '40 - 49'
        WHEN age BETWEEN 50 and 59 THEN '50 - 59'
        WHEN age BETWEEN 60 and 69 THEN '60 - 69'
        WHEN age BETWEEN 70 and 79 THEN '70 - 79'
        WHEN age >= 80 THEN 'Over 80'
        WHEN age IS NULL THEN 'Not Filled In (NULL)'
    END as age_range,
    COUNT(*) AS count

    FROM (SELECT TIMESTAMPDIFF(YEAR, birth_date, CURDATE()) AS age FROM inquiries) as derived

    GROUP BY age_range

    ORDER BY age_range

根据 Wrikken 的建议，这是一个简单的解决方案：

SELECT
    SUM(IF(age < 20,1,0)) as 'Under 20',
    SUM(IF(age BETWEEN 20 and 29,1,0)) as '20 - 29',
    SUM(IF(age BETWEEN 30 and 39,1,0)) as '30 - 39',
    SUM(IF(age BETWEEN 40 and 49,1,0)) as '40 - 49',
    SUM(IF(age BETWEEN 50 and 59,1,0)) as '50 - 59',
    SUM(IF(age BETWEEN 60 and 69,1,0)) as '60 - 69',
    SUM(IF(age BETWEEN 70 and 79,1,0)) as '70 - 79',
    SUM(IF(age >=80, 1, 0)) as 'Over 80',
    SUM(IF(age IS NULL, 1, 0)) as 'Not Filled In (NULL)'

FROM (SELECT TIMESTAMPDIFF(YEAR, birth_date, CURDATE()) AS age FROM inquiries) as derived

【问题讨论】：

您的问题已经回答了我自己的问题。谢谢你:)

标签： mysql

【解决方案1】：

范围表的替代方案（这是我的偏好），单行答案可能是：

SELECT
    SUM(IF(age < 20,1,0)) as 'Under 20',
    SUM(IF(age BETWEEN 20 and 29,1,0)) as '20 - 29',
    SUM(IF(age BETWEEN 30 and 39,1,0)) as '30 - 39',
    SUM(IF(age BETWEEN 40 and 49,1,0)) as '40 - 49',
...etc.
FROM inquiries;

【讨论】：

我刚刚尝试使用 SUM 方法，它很简单而且效果很好。它按指定的顺序放置 SUM。我已将最终解决方案放在原始问题中，以防有人想查看。

【解决方案2】：

对结果进行排序的一种方法是在 select 语句中引入一列，并为其指定您希望结果与其余部分排序的方式的排名值，然后按该行排序，例如

SELECT
CASE
    WHEN age < 20 THEN 'Under 20'
    WHEN age BETWEEN 20 and 29 THEN '20 - 29'
    WHEN age BETWEEN 30 and 39 THEN '30 - 39'
    WHEN age BETWEEN 40 and 49 THEN '40 - 49'
    WHEN age BETWEEN 50 and 59 THEN '50 - 59'
    WHEN age BETWEEN 60 and 69 THEN '60 - 69'
    WHEN age BETWEEN 70 and 79 THEN '70 - 79'
    WHEN age >= 80 THEN 'Over 80'
    WHEN age IS NULL THEN 'Not Filled In (NULL)'
END as age_range,
COUNT(*) AS count,
 CASE
    WHEN age < 20 THEN 1
    WHEN age BETWEEN 20 and 29 THEN 2
    WHEN age BETWEEN 30 and 39 THEN 3
    WHEN age BETWEEN 40 and 49 THEN 4
    WHEN age BETWEEN 50 and 59 THEN 5
    WHEN age BETWEEN 60 and 69 THEN 6
    WHEN age BETWEEN 70 and 79 THEN 7
    WHEN age >= 80 THEN 8
    WHEN age IS NULL THEN 9
END as ordinal

FROM (SELECT TIMESTAMPDIFF(YEAR, birth_date, CURDATE()) AS age FROM inquiries) as derived

GROUP BY age_range

ORDER BY ordinal

【讨论】：

【解决方案3】：

创建一个包含所有范围的表并使用外连接。
按该表另一列中的数值排序

选择范围，.... 从范围左连接（您的子查询）打开（ranges.range = your_range） ... ORDER BY range.year ASC

【讨论】：

这似乎是一个可以解决我最初的两个问题的解决方案，但是我在弄清楚 JOIN 子句时遇到了麻烦。在上面的解决方案中，“your_range”是什么？