Unpivot with column name

Question

I have a table StudentMarks with columns Name, Maths, Science, English. Data is like

Name,  Maths, Science, English  
Tilak, 90,    40,      60  
Raj,   30,    20,      10

I want to get it arranged like the following:

Name,  Subject,  Marks
Tilak, Maths,    90
Tilak, Science,  40
Tilak, English,  60

With unpivot I am able to get Name, Marks properly, but not able to get the column name in the source table to the Subject column in the desired result set.

How can I achieve this?

I have so far reached the following query (to get Name, Marks)

select Name, Marks from studentmarks
Unpivot
(
  Marks for details in (Maths, Science, English)

) as UnPvt

Solution 1

Your query is very close. You should be able to use the following which includes the subject in the final select list:

select u.name, u.subject, u.marks
from student s
unpivot
(
  marks
  for subject in (Maths, Science, English)
) u;

See SQL Fiddle with demo

Solution 2

You may also try standard sql un-pivoting method by using a sequence of logic with the following code.. The following code has 3 steps:

1. create multiple copies for each row using cross join (also creating subject column in this case)
2. create column "marks" and fill in relevant values using case expression ( ex: if subject is science then pick value from science column)

3. remove any null combinations ( if exists, table expression can be fully avoided if there are strictly no null values in base table)

    select *
    from 
    (
       select name, subject,
       case subject
       when 'Maths' then maths
       when 'Science' then science
       when 'English' then english
       end as Marks
   from studentmarks
   Cross Join (values('Maths'),('Science'),('English')) AS Subjct(Subject)
   )as D
   where marks is not null;
   

Solution 3

Another way around using cross join would be to specify column names inside cross join

select name, Subject, Marks 
from studentmarks
Cross Join (
values (Maths,'Maths'),(Science,'Science'),(English,'English')
) un(Marks, Subject)
where marks is not null;

Comments

[LBogaardt]

@bluefeet Is there a way such that you don't need to specify the names (Maths, Science, English)? I am doing this operation to many tables, all with the same structure but with different column names.

[jjjjjjjjjjj]

@LBogaardt No, you need to explicitly define the columns to include.

[Taryn]

@LBogaardt Take a look at my answer here, you could use dynamic sql to unpivot without specifying the column names.

[Cristian Scutaru]

This also works with any RDBMS! VALUES, when not available, can be replaced by a subquery with SELECT ... UNION ... SELECT ... Wondering about the performance of that CROSS JOIN though...