Tickets created and resolved (or merged) per year
SELECT * 
  FROM ( SELECT DISTINCT year(Created) AS Created
           FROM rt4.Tickets
       ) AS w

  LEFT JOIN ( SELECT year(Resolved) AS Resolved
                   , count(*) AS resolved_cnt
                FROM rt4.Tickets
               WHERE Resolved IS NOT NULL
               GROUP BY year(Resolved) 
            ) AS z
         ON z.Resolved = w.Created

  LEFT JOIN ( SELECT year(Created) AS Created
                   , count(*) AS merged_cnt
                FROM rt4.Tickets
               WHERE Merged IS NOT NULL
               GROUP BY year(Created) 
            ) AS q
         ON q.Created = w.Created
;


Sure you have to remember that functional restrictions like year() in the WHERE, JOIN...ON or GROUP BY clauses cannot be speeded up by indexes and can be VERY slow. 

I hope that query wouldn't be runned on the regular basis.