Question

Suppose I have this database table (some sample code below) that stores the relationship between two lists (requirements and testcases in my case) and I want to create a table with rows showing testcases and columns showing requirements with an indicator showing that a relationship exists.

A few limitations

• I don’t have the luxury of changing the db structure as this belongs to an open source test case management system (TestLink).
• It’s possible to write some code for this, but I’m hoping it can be done in MySQL.
• Ah, and yes, it uses MySQL, so this would have to work in that environment.

• This functionality used to exist, but has been taken out because typically, this type of work brings the db to its knees when there are tens-of-thousands of testcases and requirements.

  create table pivot (
  req_id int(11),
  testcase_id int(11)
  ) ;

  /*Data for the table pivot */

  insert into pivot(req_id,testcase_id) values (1,1);

  insert into pivot(req_id,testcase_id) values (2,2);

  insert into pivot(req_id,testcase_id) values (3,3);

  insert into pivot(req_id,testcase_id) values (4,1);

  insert into pivot(req_id,testcase_id) values (5,2);

  insert into pivot(req_id,testcase_id) values (6,3);

  insert into pivot(req_id,testcase_id) values (2,1);

  insert into pivot(req_id,testcase_id) values (3,2);

What I want to get out of the query is a table that looks somethign like this:

   1    2    3    4    5    6
1  x    x         x
2       x    x         x
3            x              x

Note:the row are the testcase_ids and the columns are the ‘req_ids’

Anyone have a tip on how to get this with just SQL?

Answer 1

I now have a name for what I’m trying to accomplish. It’s a ‘dynamic crosstab’. Here is how I got to the solution. Thanks to http://rpbouman.blogspot.com/2005/10/creating-crosstabs-in-mysql.html for the clear instructions for getting here.

Lines 1-20 – Set up a table to use for testing.

Lines 22-29 – a ‘static’ crosstab query, assuming I know how many requirements I’ve got.
Thanks D Mac for the solution you gave 🙂

Lines 30-44 – A query that dynamically generates the static query above.

Lines 45-72 – This is where I’m having the problem. The intent is to create a stored procedure that returns the result of the dynamic query. MySQL is saying there is a syntax issue, but I don’t see how to fix it. Any thoughts?

drop table if exists pivot;

create table `pivot` ( 
`req_id` int(11), 
`testcase_id` int(11) 
); 

/*Data for the table `pivot` */ 

insert into `pivot`(`req_id`,`testcase_id`) values (1,4); 
insert into `pivot`(`req_id`,`testcase_id`) values (2,4); 
insert into `pivot`(`req_id`,`testcase_id`) values (3,4); 
insert into `pivot`(`req_id`,`testcase_id`) values (4,7); 
insert into `pivot`(`req_id`,`testcase_id`) values (1,7); 
insert into `pivot`(`req_id`,`testcase_id`) values (2,12); 
insert into `pivot`(`req_id`,`testcase_id`) values (3,12); 
insert into `pivot`(`req_id`,`testcase_id`) values (4,4); 

select * from pivot;

select testcase_id
,        if(sum(req_id = 1), 1, 0)
,        if(sum(req_id = 2), 1, 0)
,        if(sum(req_id = 3), 1, 0)
,        if(sum(req_id = 4), 1, 0)
from pivot
group by testcase_id;

select concat(
      'select testcase_id','\n'
      , group_concat(
         concat(
                ',        if(sum(req_id = ',p2.req_id,'), 1, 0)','\n'
          )
          order by p2.req_id
          separator ''
        )
      , 'from pivot','\n'
      , 'group by testcase_id;','\n'
      ) statement
from pivot p2
order by p2.req_id;

CREATE PROCEDURE p_coverage()
LANGUAGE SQL
NOT DETERMINISTIC
CONTAINS SQL
SQL SECURITY DEFINER
begin
    select concat(
                  'select testcase_id','\n'
                  , group_concat(
                     concat(
                            ',        if(sum(req_id = ',p2.req_id,'), 1, 0)','\n'
                      )
                      order by p2.req_id
                      separator ''
                    )
                  , 'from pivot','\n'
                  , 'group by testcase_id;','\n'
                  ) statement
    into @coverage_query
    from pivot p2
    order by p2.req_id;

    prepare coverage from @coverage_query;

    execute coverage;

    deallocate prepare coverage;
end;

select * from pivot;