hive union all same table

[zhangjp]

Hi  I want to query table_a by different where clause as follow
  select * from (      select  col1, count(1) from table_a where col2 ='xx' 
group by col1             union all     select  col1, count(1) from table_a 
where col2 ='xx' group by col1             union all      select  col1, 
count(1) from table_a where col2 ='xx' group by col1     )
I found the total jobs is 4， is there any optimiztion?  I think it should scan 
table_a once and only one job