SELECT *,GROUP_CONCAT(execute.exefio ORDER BY execute.exenum SEPARATOR '\n') as exe 
FROM register  LEFT JOIN execute ON register.docid = execute.docid 
 WHERE (register.docid<>0) AND (datecreate between '2018-09-01' AND '2018-09-28')
 AND (exe LIKE '%Мигован А.К.%') GROUP BY register.docid

SELECT *,GROUP_CONCAT(execute.exefio ORDER BY execute.exenum SEPARATOR '\n') as exe 
FROM register  LEFT JOIN execute ON register.docid = execute.docid 
 WHERE (register.docid<>0) AND (datecreate between '2018-09-01' AND '2018-09-28')
GROUP BY register.docid