Question

我有一张像这样的表格 -

Students                Class1               Class2                   Class3
student1                 1                      0                       1
student2                 0                      1                       0
student3                 1                      1                       0
studnet4                 0                      1                       1

我想要像这样输出 -

Class1 has 3 Students

Class2 has 2 Students

Class3 has 3 Students

我已经对此进行了查询 -

select classname||' has '||count(num)||' students 'as no_of_students from
(
select * from enroll )
unpivot (
num for classname in (class1,class2,class3)
) 
where num=1
group by classname;

但是，如果我的in子句中每次更改的课程数量都多于其他课程。我也不知道pl / sql。那么，如果有人可以提供帮助吗？

Answer 1

-- it is an old-school solution, but it worked for me
-- step 1
create or replace procedure test_students
as

cursor c_cols
is
select column_name
from user_tab_columns
where table_name = 'ENROLL'
and column_name != 'STUDENTS';

l_number_of_students number;
l_my_col user_tab_columns.column_name%type;
l_statement varchar2(30000);

begin



 for r_cols in c_cols loop

 l_my_col := r_cols.column_name; 

 l_statement :=
 ' select sum('||l_my_col||')
   from enroll ';

 execute immediate l_statement into  l_number_of_students;

 dbms_output.put_line ('Number of students: '||l_number_of_students ||'in Class :'||l_my_col);

 end loop;




end; 

-- step 2
begin
test_students;
end;
/

如何动态切换

1 个答案: