Question

我已经绞尽脑汁待了两天。我需要计算每个年龄段的成员，但无法弄清楚如何。我已经做到这一点，但这仅显示了成员的年龄组，但不计算它们。

SELECT
CASE
    WHEN YEAR(CURRENT_DATE()) - YEAR(birth_date) - (RIGHT(CURRENT_DATE(), 5) < RIGHT (birth_date, 5)) BETWEEN 12 AND 18 THEN '12-18'
    WHEN YEAR(CURRENT_DATE()) - YEAR(birth_date) - (RIGHT(CURRENT_DATE(), 5) < RIGHT (birth_date, 5)) BETWEEN 19 AND 55 then '19-55'
ELSE '56 or older'
END AS age_group
FROM members
ORDER BY age_group

Answer 1

您需要告诉查询执行计数。您还需要按要计算的字段进行分组。

试试这个：

select count(*) as the_count, 
  case
    when YEAR(CURRENT_DATE()) - YEAR(birth_date) - (RIGHT(CURRENT_DATE(), 5) < RIGHT (birth_date, 5)) between 12 AND 18 THEN '12-18' 
    when YEAR(CURRENT_DATE()) - YEAR(birth_date) - (RIGHT(CURRENT_DATE(), 5) < RIGHT (birth_date, 5)) between 19 AND 55 then '19-55' 
    else '56 or older'
  end
  as age_group
from members group by age_group order by age_group;

点击以下链接查看正在运行的演示：

SQLFiddle

Answer 2

您已经提取了所需的数据。要对其进行计数，请将其作为子查询嵌入，并通过group by子句计算每个组的结果。通过为子查询中的每个成员添加唯一标识符，它允许每个组中的成员计数在组中生存（即，不会折叠为每个组的单个行）。

SELECT age_group, COUNT(*) AS group_count
FROM
    (SELECT
        - -  add a unique identifier for each member here as a select attribute, 
        CASE 
            WHEN YEAR(CURRENT_DATE()) -  YEAR(birth_date) - (RIGHT(CURRENT_DATE(), 5) < RIGHT (birth_date, 5)) BETWEEN 12 AND 18 THEN '12-18' 
            WHEN YEAR(CURRENT_DATE()) - YEAR(birth_date) - (RIGHT(CURRENT_DATE(), 5) < RIGHT (birth_date, 5)) BETWEEN 19 AND 55 then '19-55' ELSE '56 or older' END AS age_group 
    FROM members) AS tab_age_groups
GROUP BY age_group
ORDER BY age_group;

非常沮丧的mysql计数功能

2 个答案: