存储过程中,如何把多个select结果,合并成一个结果集返回

存储过程中,怎么把多个select结果,合并成一个结果集返回?
select userid,username,price,vol from table_a ...
select userid,username,price,vol from table_b...


要让这两句形成一个结果集。怎么办?

------解决方案--------------------
select userid,username,price,vol from table_a ...
union all
select userid,username,price,vol from table_b...

------解决方案--------------------
SQL code

select userid,username,price,vol from table_a ...
union all--不去掉上下两语句的重复行
select userid,username,price,vol from table_b...


select userid,username,price,vol from table_a ...
union--去掉上下两语句的重复行
select userid,username,price,vol from table_b...

------解决方案--------------------
select userid,username,price,vol from table_a ...
union all
select userid,username,price,vol from table_b...