Question

我的查询有问题。

我有这样一张桌子： tbl_people

id | startDate  | endDate    | Gender
1  | 2010-03-01 | 2011-04-11 | m
2  | 2010-04-01 | 2010-06-14 | f
3  | 2010-03-01 | 2010-04-11 | m
4  | 2009-09-09 | 2009-10-10 | f

对于数据库中给出的所有年份，我想计算人的性别，因为那一年是在startDate和endDate之间。当startDate是2010年和endDate 2011时，它应该计入两者。

所以结果应该是这样的：

year | m | f | m+f
2009 | 0 | 1 | 1
2010 | 2 | 1 | 3
2011 | 1 | 0 | 1

我不知道如何实现查询所有年份的列表。目前我有这个：

select
    sum(case tbl_people.Gender when 'm' then 1 else 0 end),
    sum(case tbl_people.Gender when 'f' then 1 else 0 end),
    count( tbl_people.Gender )
...

祝你好运

Answer 1

您需要加入包含所有年份的表格。您可以创建包含所有年份的真实表，也可以在子查询中动态构建它：

SELECT y.year, 
        SUM(p.Gender = 'm') AS m,
        SUM(p.Gender = 'f') AS f,
        COUNT(*) AS `m+f`
FROM (SELECT 2009 AS year
      UNION
      SELECT 2010 AS year
      UNION
      SELECT 2011 AS year) AS y
LEFT JOIN tbl_people AS p ON y.year BETWEEN YEAR(p.startDate) AND YEAR(p.endDate)
GROUP BY y.year

DEMO

Mysql计数和特定日期之间的组

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