UNION
If R1 and R2 are two union compatible relations then R3 = R1 ∪ R2 is the relation having tuples that are either in R1 or in R2 or in both.
In case, R3 will have tuples such that R3 = {t | R1 ∋ t ∨ R2 ∋ t}.
Example
R1
X
Y
A1
B1
A7
B7
A2
B2
A4
B4
R2
A
B
A3
B3
R3 = R1 ∪ R2 is
Q
Note: 1) Union is a commutative operation, i.e, R ∪ S = S ∪ R.
2) Union is an associative operation, i.e.
R ∪ (S ∪ T) = (R ∪ S) ∪ T.