Union - basic set operation, Database Management System

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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

X	Y
A1	B1
A7	B7
A2	B2
A4	B4

A	B
A1	B1
A2	B2
A3	B3
A4	B4

R3 = R1 ∪ R2 is

A	B
A1	B1
A2	B2
A3	B3
A4	B4
A7	B7

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.

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