看似簡單的一道SQL面試題，你是否能夠很快寫出答案？

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  近期在群裡面看到了如下這樣一個面試題目，這個題目其實難度不大，但是你是否能夠很快寫出這個答案來呢？

建表語句

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

插入資料

insert into student values
("201901","張大佬","男","1985","計算機系","北京市海澱區"),
("201902","郭大俠","男","1986","中文系","北京市昌平區"),
("201903","張三","女","1990","中文系","湖南省永州市"),
("201904","李四","男","1990","英語系","遼甯市阜新市"),
("201905","王五","女","1991","英語系","福建省廈門市"),
("201906","王六","男","1988","計算機系","湖南省衡陽市");      

結果如下

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;      

結果如下

第二步

select 
        院系,
        sum(男) 男,
        sum(女) 女,
        sum(男) + sum(女) as 總計
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;      

結果如下