text: #PROBLEM 2
  SELECT repository_id,contributor_id FROM repositories_contributors
  WHERE  repository_id = contributor_id
  ORDER BY id ASC;
  
  #PROBLEM 3
  SELECT i.id, CONCAT(u.username, ' : ', i.title) AS 'issue_assignee' FROM users AS u
  JOIN issues AS i
  WHERE u.id = i.assignee_id
  ORDER BY i.id DESC;
  
  #PROBLEM 4
  SELECT f.id, f.name as Name, CONCAT(f.size, 'KB') as size FROM files AS f
  WHERE NOT EXISTS( SELECT p.parent_id FROM files AS p
  				   WHERE p.parent_id = f.id
  				)
  ORDER BY f.id;
  
  #PROBLEM 5
  SELECT r.id, r.name, COUNT(DISTINCT i.id) AS `issues` FROM repositories AS r
  JOIN issues AS i
  ON i.repository_id = r.id
  GROUP BY r.id
  ORDER BY `issues` DESC, r.id ASC
  LIMIT 5;
  
  #PROBLEM 6
  SELECT 
      rc.repository_id,
  	r.name, 
  	COUNT(DISTINCT c.id) AS `commits`, 
  	COUNT(DISTINCT rc.contributor_id) AS `contributors` 
  FROM repositories_contributors AS rc
  JOIN repositories AS r
  ON rc.repository_id = r.id
  JOIN commits AS c
  ON r.id = c.repository_id
  GROUP BY rc.repository_id
  ORDER BY `contributors` DESC, r.id ASC
  LIMIT 1;
  
  
  #PROBLEM 7	
  SELECT r.id, r.name, COUNT(DISTINCT c.contributor_id)  AS `users` FROM commits AS c
  RIGHT JOIN repositories AS r
  ON c.repository_id = r.id
  GROUP BY r.id
  ORDER BY `users` DESC,r.id ASC;
  