Question

我试图在SQL Server中编写一个查询，它会给我一些关于我所拥有的表的信息。我有2张表/样本数据：

人

pid     surname gender
196     Kelly   F
248     Hoskin  M
375     Walker  M

度

pid     title                   is_doctoral
196     Master of Science       1
248     Doctor of Philosophy    0

我想要的结果是对男性和女性信息的一些分析：

结果

Gender      # Students  Doctorate Degrees Held      Master Degrees Held         Graduation Rate
Males       2           1                           0                           50%
Females     1           0                           1                           100%

我无法弄清楚如何在结果表（男性，女性）中创建自定义第一列，我不知道如何进行条件求和。我是SQL的初学者，非常感谢任何帮助。有人可以创建一个查询来获得该结果吗？如果我看到查询，我将能够从那里了解它。

Answer 1

试试这个：

示例数据

create table person(
    pid int,
    surname varchar(50),
    gender char(1)
)
create table degree(
    pid int,
    title varchar(50),
    is_doctoral varchar(5)
)
insert into person values
(196, 'Kelly', 'F'),
(248, 'Hoskin', 'M'),
(375, 'Walker', 'M')
insert into degree values
(196, 'Master of Science', 'TRUE'),
(248, 'Doctor of Philosophy', 'FALSE');

<强>解

select
    case when p.gender = 'F' then 'Female' else 'Male'end as Gender,
    count(*) as [# of Students],
    sum(case when d.is_doctoral = 'TRUE' then 1 else 0 end) as [Doctorate Degrees Held],
    sum(case when d.is_doctoral = 'FALSE' then 1 else 0 end) as [Masters Degrees Held],
    convert(varchar(10), (cast((count(d.pid) * 1.0)/count(*) * 100 as decimal))) + '%' as [Graduation Rate]
from person p
left join degree d
    on d.pid = p.pid
group by p.gender
order by p.gender desc

Answer 2

我相信您正在寻找case statement

SELECT
CASE gender
  WHEN 'M' THEN 'Male'
  WHEN 'F' THEN 'Female'
END as string_gender
FROM person;

使用自定义列的SQL查询

2 个答案: