我在查询时遇到问题。
我有一张这样的桌子：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，我想计算人们的性别，该年份在开始日期和结束日期之间。当 startDate 为 2010 年且 endDate 为 2011 时，它应该同时计入两者。
所以结果应该看起来像这样：
year | m | f | m+f
2009 | 0 | 1 | 1
2010 | 2 | 1 | 3
2011 | 1 | 0 | 1
我真的不知道如何实现对所有年份列表的查询。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 )
...
此致敬意
您需要使用包含所有年份的表进行联接。您可以创建一个包含所有年份的真实表，也可以在子查询中动态构造它：
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
演示