The difference between union and group is as follows:

★ Take two tables t1 and t2.

★ In t1 we have columns like a,b,c,d. and t2 has a,d,e,f.

★ Ao union means t1 union t2 i.e getting result from both tables i.e a,b,c,d,e.,f

★ Where as group performs on a individual column in a particular table.