这个怎么做，用union和group

select id ,sum(num) as num from (select * from a表 union all select * from b表) a
group by id

create table uniona(id varchar(4) not null,num int not null)insert into uniona(id,num) values('a',18);insert into uniona(id,num) values('b',15);insert into uniona(id,num) values('c',31);insert into uniona(id,num) values('d',23);insert into uniona(id,num) values('w',3);create table unionb(id varchar(4) not null,num int not null)insert into unionb(id,num) values('a',8);insert into unionb(id,num) values('c',3);insert into unionb(id,num) values('d',3);insert into unionb(id,num) values('w',13);select t.id as ID,sum(t.num) as NUM from(select id,num from uniona as a union select id,num from unionb as b) tgroup by t.id