看似简单的一道SQL面试题，你是否能够很快写出答案？

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  近期在群里面看到了如下这样一个面试题目，这个题目其实难度不大，但是你是否能够很快写出这个答案来呢？

建表语句

create table student (
    	id varchar(20),
    	name varchar(20),
    	gender char(1),
    	birth varchar(20),
    	department varchar(20),
    	address varchar(20)
) charset = utf8;

插入数据

insert into student values
("201901","张大佬","男","1985","计算机系","北京市海淀区"),
("201902","郭大侠","男","1986","中文系","北京市昌平区"),
("201903","张三","女","1990","中文系","湖南省永州市"),
("201904","李四","男","1990","英语系","辽宁市阜新市"),
("201905","王五","女","1991","英语系","福建省厦门市"),
("201906","王六","男","1988","计算机系","湖南省衡阳市");

结果如下

第一步

select 
    department 院系,
    case gender when "男" then 1 else 0 end 男,
    case gender when "女" then 1 else 0 end 女
from student;

结果如下

第二步

select 
    	院系,
    	sum(男) 男,
    	sum(女) 女,
    	sum(男) + sum(女) as 总计
from
(
    select department 院系,
    case gender when "男" then 1 else 0 end 男,
    case gender when "女" then 1 else 0 end 女
    from student
) a
group by 院系;

结果如下