here's the query for concatinating the lastname and firstname in name field:
update clients set name = concat(firstname, ' ', lastname)
(or)
update clients set name = concat(lastname, ' ', firstname)
(or Where data has been added to a existing list)
update clients set name=concat(firstname,' ',lastname)
where name is null and length(firstname)>0 or length(lastname)>0
limit 2000000