Relational Table

Question

Suppose there are 2 relation S and R . S is Non-empty relation and R is an empty relation. How Cartesian product of two tables returns NULL?

I think join not possible both tables. As NULL table cannot satisfy any condition.rt?

Comments

@Shaik

suppose a condition S is non empty and R has 1 tuple, then what $S\times R$ will return?

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Cartesian product always return m*n rows

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@srestha

shaik is correct..!

Answer 1

The Cartesian product returns all the rows in all the tables listed in the query.  Each row in the first table is paired with all the rows in the second table. So if  S is non-empty and R is empty as per your question, it would return n(no. of rows in S) X zero(i.e.no of rows in table R = 0 rows