Query many-to-many in SQL

Question

I've got a little question about an SQL Query I'm trying to do. My schema is a basic one holding users and questions like so
User
ID
UserName
Question
ID
Question
Answer
User_ID :
Question_ID :
Answer
The basic idea is to give an extendability to add new questions on the fly, so now I'm trying to build a joined query that will return all the users, and all the questions, and the users answers to the questions
something like.
|--------------------------------------------------------------------------
| UserName | Question1 | Question2 | Question3 |
| Scott | answer1 | dog | NULL |
I know you'd generally edit the USER table to include these answers, but I'd just like to know if this style is possible (I don't want to dynamically edit the tables after the application is deployed)

Answer 1

SQL does not allow one to create a dynamic result with variable columns. E.g. using your example:
UserA | Question1 | Question2 | Question3 |
UserB | Question1 | Question2
UserC | Question1 | Question2 | Question3 | Question 4This is not valid as as some rows have more columns than other rows.
The return of a SQL SELECT is called the SQL projection. The projection is fixed - in other words, the same projection needs to apply to all rows.
The projections can be complex and use object classes and subclasses. For example a projection can include an object type column of an abstract object class for animals - and there can be a mix of different animals (sub-classed) returned by the select, e.g. a couple of rows for dogs, a few cats and a horse and a cow. But this uses object relational design and concepts which are not the norm.. and likely not applicable to you.
Another complex projection type is using collections (aka arrays). A projected column can be an array and can contain zero or more values. This can be used to return a USERNAME column, followed by a collection that contains the questions (and/or answers) for that specific user.
A basic example. Projection that shows the department and a collection of employees in that department.
SQL> create or replace type TStrings is table of varchar2(4000);
  2  /                                                         
Type created.
SQL>
SQL>
SQL> select                     
  2          d.dname,           
  3          cast( multiSet( select e.ename from emp e where e.deptno = d.deptno order by 1) as TStrings ) as EMPLOYEE_LIST
  4  from       dept d                                                                                                    
  5  order by d.dname                                                                                                     
  6  /                                                                                                                    
DNAME                EMPLOYEE_LIST
ACCOUNTING           TSTRINGS('CLARK', 'KING', 'MILLER')                                            
OPERATIONS           TSTRINGS()                                                                     
RESEARCH             TSTRINGS('ADAMS', 'FORD', 'JONES', 'SCOTT', 'SMITH')                           
SALES                TSTRINGS('ALLEN', 'BLAKE', 'JAMES', 'MARTIN', 'TURNER', 'WARD')                
SQL>You should however question how necessary this approach is. As the same thing can be achieved using a normal join - and control break processing in the client to process and render the data set as required.
Always make sure that the technical solution fits the actual problem.