Question

How do i return multiple columns from a table ?

My Course table:

| Course | PersId | Taskid | Status |

Computer < > User1 <> 1 < > confirmed
Computer < >User2 <> 1 <> unconfirmed

Computer < >User3 <> 1 <> unconfirmed

Computer < >User1 <> 2 <> confirmed

Computer < >User2 <> 2 <> confirmed

Computer < >User3 <> 2 <> unconfirmed

I want it to return like this:

| PersId | Task_1 | Task_2 |

User1 <> confirmed < > confirmed

User2 <> unconfirmed <> confirmed

User3 <> unconfirmed <> unconfirmed

Question 2:
There are other courses(math, english etc) in my table with more tasks than two. Do i need to use some kind of iteration to return the task columns ? because i dont want to make a SQL query for each single course(over 100).

thanks in advance

Answer 1

You can use a CASE and an aggregate:

select persid,
  max(case when taskid = 1 then status end) as Task1,
  max(case when taskid = 2 then status end) as Task2
from course
group by persid

If you want to include the course info:

select persid,
  course,
  max(case when taskid = '1' then status end) as Task1,
  max(case when taskid = '2' then status end) as Task2
from course
group by persid, course
order by course, persid

See SQL Fiddle with Demo

If you have an unknown number of tasks, then you can use a prepared statement to generate this dynamically:

SET @sql = NULL;
SELECT
  GROUP_CONCAT(DISTINCT
    CONCAT(
      'max(case when taskid = ''',
      taskid,
      ''' then status end) AS Task_',
      taskid
    )
  ) INTO @sql
FROM course;

SET @sql = CONCAT('SELECT persid, course, ', @sql, ' 
                  FROM course 
                  group by persid, course
                  order by course, persid');

PREPARE stmt FROM @sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;

See SQL Fiddle with Demo