SQL拆分列

Question

我做了一个简单的例子来更好地理解我的问题是什么。 所以，我有2个表，我有一个基于inner join的选择，这是一个选择。

create table students(
id_student number,
name_student varchar2(15),
id_advisor number,
money number
);

insert into students values(1, 'Student_1', 1, 100);
insert into students values(2, 'Student_2', 8,-200);
insert into students values(4, 'Student_4', 7, 256);
insert into students values(5, 'Student_5', 3, -305);   
----------------

create table advisors(
id_advisor number,
name_advisor varchar2(15)
);

insert into advisors values(1, 'advisor_1');
insert into advisors values(3, 'advisor_3'); 
insert into advisors values(5, 'advisor_5');

------------------------------------------
SELECT name_advisor, money as money_pozitive
FROM(
select name_student, name_advisor, money from students 
inner join advisors on students.id_advisor = advisors.id_advisor)
WHERE money > 0 

使用此代码，我得到以下结果：

name_advisor    |    money_pozitive
------------------------------------
advisor_1       |    100

我的问题是，我如何添加名为money_negative的额外列，当然还有负值？像这样：

name_advisor    |    money_pozitive    |  money_negative
---------------------------------------------------------
advisor_1       |    100               |  -305

Answer 1

只需使用case：

select name_student, name_advisor,
       (case when money > 0 then money end) as money_positive,
       (case when money < 0 then money end) as money_negative
from students s inner join
     advisors a
     on s.id_advisor = a.id_advisor;

注意：

• 不需要子查询。
• 使用表别名。这些使查询更容易编写和阅读。
• 如果您有多个表名，那么限定所有列名是一个好习惯（即，使用表别名作为列名）。
• 而且您不需要where条款。