下面是项目中按照男女年龄段统计的核心sql代码:

                COUNT(tr.id)AS '体检总人数',
		SUM(CASE WHEN s.sex=1 THEN 1 ELSE 0 END) AS '男体检总数',
		SUM(CASE WHEN s.sex=0 THEN 1 ELSE 0 END) AS '女体检总数',
		
		SUM(CASE WHEN s.sex=1 AND tr.age >=18 AND tr.age <=29 THEN 1 ELSE 0 END) AS '男18--29岁',
		SUM(CASE WHEN s.sex=0 AND tr.age >=18 AND tr.age<=29 THEN 1 ELSE 0 END) AS '女18--29岁',
		
		SUM(CASE WHEN s.sex=1 AND tr.age <=45 AND tr.age>=30 THEN 1 ELSE 0 END) AS '男30--39岁',
		SUM(CASE WHEN s.sex=0 AND tr.age<=45  AND tr.age>=30  THEN 1 ELSE 0 END) AS '女30--39岁',
		
		SUM(CASE WHEN s.sex=1 AND tr.age <=50 AND tr.age>=46 THEN 1 ELSE 0 END) AS  '男40--49岁',
		SUM(CASE WHEN s.sex=0 AND tr.age<=50 AND tr.age>=46 THEN 1 ELSE 0 END) AS  '女40--49岁',
		
		SUM(CASE WHEN s.sex=1 AND tr.age <=60 AND tr.age>50 THEN 1 ELSE 0 END) AS  '男50--59岁',
		SUM(CASE WHEN s.sex=0 AND tr.age<=60 AND tr.age>50 THEN 1 ELSE 0 END) AS  '女50--59岁',
		
		SUM(CASE WHEN s.sex=1 AND tr.age <=70 AND tr.age>60 THEN 1 ELSE 0 END) AS  '男60--69岁',
		SUM(CASE WHEN s.sex=0 AND tr.age<=70 AND tr.age>60 THEN 1 ELSE 0 END) AS  '女60--69岁',
		
		SUM(CASE WHEN s.sex=1 AND tr.age <=80 AND tr.age>70 THEN 1 ELSE 0 END) AS  '男70--79岁',
		SUM(CASE WHEN s.sex=0 AND tr.age<=80 AND tr.age>70 THEN 1 ELSE 0 END) AS  '女70--79岁',
		
		SUM(CASE WHEN s.sex=1 AND tr.age >80 THEN 1 ELSE 0 END) AS  '男80岁以上',
		SUM(CASE WHEN s.sex=0 AND tr.age>80 THEN 1 ELSE 0 END) AS  '女80岁以上'

我拿其中一句解释一下

SUM(CASE WHEN s.sex=1 AND tr.age >=18 AND tr.age <=29 THEN 1 ELSE 0 END) AS '男18--29岁',

先看sum的括号里面的部分

case when sex = 1 and age>=18 and age <=29 then 1 else 0 end

它表示的含义是:如果性别为1(也就是男),并且年龄在18-29岁之间成立为1,不成立为0.

case和end 是一个关键字你可以理解为语句的开始和结束。

when相当于if做判断,then就是判断之后显示的结果。如果成立显示为1,不成立显示为0

sum就是将各个值相加。形如:1+1+0+1+0+1+1+0+1+1

项目最后统计的结果截图形如: