Two relations(tables) are said be union compatible if:-
- Both have the same number of attributes (columns)
- Corresponding attributes are of the same type.
- Duplicate tuples should be automatically removed.
let suppose there are two relations or tables R and S and
.......// Cardinality of R means the number of rows or tuples in R
then the number of tuples is given by this
|Left join ⟕||m||mn|
|Right Join ⟖||n||mn|
|Full Join ⟗||(m+n )or max(m,n)||mn|
Consider the join of a relation R with a relation S. If R has m tuples and S has n tuples then the maximum and minimum sizes of the join respectively are:-
maximum size means all the common attribute value in R is mapped with each value of the common attribute in S, So total is mn
for minimum: nothing is matched. So 0