select count() as b from table_1
union all
select count() as b from table_2
) as a（注意这里要取个别名）
本文转自 Lee_吉 博客，原文链接： http://blog.51cto.com/12173069/2053757 如需转载请自行联系原作者
union all查询统计总数量
select sum(a.b) as num from (
select count() as b from table_1
union all
select count() as b from table_2
select count() as b from table_1
union all
select count() as b from table_2