I am having doubt in UNION concept . Suppose there are three sub-queries .
select * from a where some cond
select * from b where some cond
select * from c where some cond
If first query gives you 1 result set ,second & third query gives you none ..
What should be the output after UNION?
As per my understanding , output after UNION should be 1 result set which was retrieved from first query..
Please help me out