union vs unionAll

There is a difference between Union and UnionAll for UnionType enum. Here is the simple example of UnionAll and Union.

lets suppose we have two sets (tables).
A = {a, b, c, e, f}, B = {g, h, i, j, k, f, c}

In the example above you can see 'f' and 'c' are common in both sets.

So, If we take Union the result would be

A Union B = {a, b,c, e, f, g, h, i, j, k}

Here you can see nothing is repeated but if we take UnionAll it will repeat both in a result set.

A UnionAll B = {a,b,c,e,f,g,h,i,j,k,f,c}