Union - basic set operation, Database Management System

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

A1

B1

A2

B2

A3

B3

A4

B4

R3 = R1 ∪ R2 is

 Q

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.

Posted Date: 3/6/2013 5:43:59 AM | Location : United States







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