union 分页问题

(SELECT a FROM tbl_name_a WHERE a=10 AND B=1)
UNION
(SELECT a FROM tbl_name_b WHERE a=11 AND B=2)
ORDER BY a LIMIT 10;
		

select * from (
	select a from tbl_name_a WHERE a=10 AND B=1
	union all
	select a from tbl_name_b WHERE a=10 AND B=1
) tbl_name
order by a limit 0,1;
		

select a,b from tbl_name_a WHERE a=10 AND B=1
union all
select a,b from tbl_name_b WHERE a=10 AND B=1