data base management system

Question

Consider a scenario, there are three tables name ‘X’, ‘Y ‘and’ Z’ with schemes X (u, v, w), Y (l, u, m, n, o, p) and Z (r, s, t, u, q), These tables have a common attribute or field. We want to retrieve the data from these tables.

In this scenario, discuss which join operation can help to retrieve the records from multiple tables. Justify your answer with at least two solid arguments.

Answer 1

Inner Join:

An inner join retrieves records that have matching values in both tables being joined. It returns only the intersecting rows, excluding non-matching ones.

In our case, we can perform an inner join on the common attribute ‘u’ between tables X and Y. The query would be:

SELECT *

FROM X

INNER JOIN Y ON X.u = Y.u;

This join ensures that only rows with matching ‘u’ values from both tables are included in the result.

Natural Join:

A natural join is a variant of inner join where the join condition is implicit based on common column names between tables.

However, natural join can be tricky when multiple common attributes exist. It implicitly matches all common columns, which might not always be desired.

In our case, a natural join between X and Y would consider both ‘u’ and ‘v’ as common attributes, which could lead to unexpected results.

Example query:

SELECT *

FROM X

NATURAL JOIN Y;

Since ‘u’ and ‘v’ are both common attributes, this join might not yield the desired outcome.