Question

这是我创建的视图

SELECT YEAR(CURRENT_TIMESTAMP) - YEAR(c.date_of_birth) - (RIGHT(CURRENT_TIMESTAMP, 5) < RIGHT(c.date_of_birth, 5)) as age, count(a.id) as occurences, a.celex_id,

COUNT(CASE WHEN c.gender = 'MALE' THEN c.id END) as males,
COUNT(CASE WHEN c.gender = 'FEMALE' THEN c.id END) as females,
COUNT(CASE WHEN c.gender IS NULL THEN c.id END) as unknowns

FROM consumer c, account a

WHERE a.consumer_id = c.id

GROUP BY age, a.celex_id;

这导致：

age | occurences | celex_id | male | female | unknowns
------------------------------------------------------
16  | 1          | 1        | 0    | 1      | 0
65  | 1          | 1        | 1    | 0      | 0
66  | 1          | 1        | 0    | 1      | 0
69  | 1          | 1        | 0    | 0      | 1

等等。

现在，我已经用case语句进行了查询，但我无法按案例分组，这是查询

SELECT
CASE
    WHEN age BETWEEN 0  AND 10 THEN '0-10'
    WHEN age BETWEEN 11 AND 20 THEN '11-20'
    WHEN age BETWEEN 21 AND 30 THEN '21-30'
    WHEN age BETWEEN 31 AND 40 THEN '31-40'
    WHEN age BETWEEN 41 AND 50 THEN '41-50'
    WHEN age BETWEEN 51 AND 60 THEN '51-60'
    WHEN age BETWEEN 61 AND 70 THEN '61-70'
    WHEN age BETWEEN 71 AND 80 THEN '71-80'
    WHEN age BETWEEN 81 AND 90 THEN '81-90'
    WHEN age BETWEEN 91 AND 100 THEN '91-100'
    WHEN age > 100 THEN 'Greater than 100'
ELSE 'Unknown'
END AS age_range, males, females, unknowns
FROM age_gender_occurences
WHERE celex_id = 1
GROUP BY age_range, males, females, unknowns

这给出了

age_range | males | females | unknowns
--------------------------------------
11-20     | 0     | 1       | 0
21-30     | 0     | 1       | 0
61-70     | 0     | 1       | 0
61-70     | 1     | 0       | 0
61-70     | 0     | 0       | 1

我已尝试直接在GROUP BY子句中复制case语句，但这不起作用。有人可以说明如何让age_range成为一个单行者吗？（比如61-70变为1行而不是3行）

Answer 1

您缺少聚合功能。我会用原始表格来写这个：

SELECT (CASE WHEN age BETWEEN 0  AND 10 THEN '0-10'
             WHEN age BETWEEN 11 AND 20 THEN '11-20'
             WHEN age BETWEEN 21 AND 30 THEN '21-30'
             WHEN age BETWEEN 31 AND 40 THEN '31-40'
             WHEN age BETWEEN 41 AND 50 THEN '41-50'
             WHEN age BETWEEN 51 AND 60 THEN '51-60'
             WHEN age BETWEEN 61 AND 70 THEN '61-70'
             WHEN age BETWEEN 71 AND 80 THEN '71-80'
             WHEN age BETWEEN 81 AND 90 THEN '81-90'
             WHEN age BETWEEN 91 AND 100 THEN '91-100'
             WHEN age > 100 THEN 'Greater than 100'
             ELSE 'Unknown'
         END) AS age_range,
        SUM(CASE WHEN c.gender = 'MALE' THEN 1 ELSE 0 END) as males,
        SUM(CASE WHEN c.gender = 'FEMALE' THEN 1 ELSE 0 END) as females,
        SUM(CASE WHEN c.gender IS NULL THEN 1 ELSE 0 END) as unknowns
FROM consumer c JOIN
     account a
     ON a.consumer_id = c.id
WHERE celex_id = 1
GROUP BY age_range;

如果你想根据视图（看起来有点过分）来写它：

SELECT (CASE WHEN age BETWEEN 0  AND 10 THEN '0-10'
             WHEN age BETWEEN 11 AND 20 THEN '11-20'
             WHEN age BETWEEN 21 AND 30 THEN '21-30'
             WHEN age BETWEEN 31 AND 40 THEN '31-40'
             WHEN age BETWEEN 41 AND 50 THEN '41-50'
             WHEN age BETWEEN 51 AND 60 THEN '51-60'
             WHEN age BETWEEN 61 AND 70 THEN '61-70'
             WHEN age BETWEEN 71 AND 80 THEN '71-80'
             WHEN age BETWEEN 81 AND 90 THEN '81-90'
             WHEN age BETWEEN 91 AND 100 THEN '91-100'
             WHEN age > 100 THEN 'Greater than 100'
             ELSE 'Unknown'
         END) AS age_range,
        SUM(males) as males,
        SUM(females) as females,
        SUM(unknowns) as unknowns
FROM age_gender_occurences
WHERE celex_id = 1
GROUP BY age_range;

换句话说，您需要再次聚合。事实上，在这种情况下，MySQL会做两个聚合，这就是为什么我推荐使用原始表格的简单版本。

当值来自case语句时，无法将列分组为相等的值

1 个答案: