MySQL UPDATE and SELECT in one pass

Question

I have a MySQL table of tasks to perform, each row having parameters for a single task.
There are many worker apps (possibly on different machines), performing tasks in

Answer 1

You may create a procedure that does it:

CREATE PROCEDURE prc_get_task (in_guid BINARY(16), OUT out_params VARCHAR(200))
BEGIN

  DECLARE task_id INT;

  SELECT id, out_params
  INTO task_id, out_params
  FROM tasks
  WHERE guid = 0
  LIMIT 1
  FOR UPDATE;

  UPDATE task
  SET guid = in_guid
  WHERE id = task_id;

END;

BEGIN TRANSACTION;

CALL prc_get_task(@guid, @params);

COMMIT;