Tasks.txt

SELECT
   Tasks.id_Task,
   Tasks.Name,
   Tasks.Description,
   Tasks.id_Worker,
   Tasks.id_Chief,
   Workers.Name AS Worker,
   Chief.Name AS Chief, 
   Tasks.Date

FROM Tasks
   LEFT JOIN (SELECT 
      Workers.id_Worker,
      Workers.Name,
      Posts.Name AS Post
  FROM Workers
      LEFT JOIN (SELECT Posts.id_Post, Posts.Name FROM Posts) Posts ON Posts.id_Post=Workers.id_Post
) Workers ON Workers.id_Worker=Tasks.id_Worker
   LEFT JOIN (SELECT 
      Workers.id_Worker,
      Workers.Name,
      Posts.Name AS Post
  FROM Workers
      LEFT JOIN (SELECT Posts.id_Post, Posts.Name FROM Posts WHERE Posts.id_Post=1) Posts ON Posts.id_Post=Workers.id_Post
WHERE Posts.Name is not null) Chief ON Chief.id_Worker=Tasks.id_Chief