drop table if exists test;

create table test (fld varchar(32));
insert into test (fld)
select 'one space' union all
select 'two  spases --' union all
select 'space _underline' union all
select 'one_underline' union all
select ' l-space' union all
select 'r-underline_' union all
select 'none' ;

drop procedure if exists multiremove;

delimiter @@

create procedure multiremove(charstodelete text) 
begin
while length(charstodelete)>0 do
	begin
	set @onechar = substring(charstodelete,1,1);
	set charstodelete = substring(charstodelete,2,length(charstodelete));
	set @sql=CONCAT("update test set fld=replace(fld,\'",@onechar,"\',\'\');");
--	select @sql;
	prepare stmt from @sql;
	execute stmt;
	deallocate prepare stmt;
	set @sql='';
	set @onechar='';
	end;
end while;
end;@@

delimiter ;

select concat("\'",fld,"\'") from test;
call multiremove(' _');
select concat("\'",fld,"\'") from test;

drop procedure multiremove;
drop table test;