如何UNPIVOT動態

Question

我有一個表像註冊這 -

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

而且我要像這 -

Class1 has 3 Students 

Class2 has 2 Students 

Class3 has 3 Students 

我輸出我已經做了查詢，像這個 -

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，如果有更多的班級比我每次在我的子句中都有變化。我也不知道pl/sql。所以如果有人可以幫忙？

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; 
/