Question

Why is the following query not valid as a natural join?

SELECT name, name, name, name
FROM customer
NATURAL JOIN employee;
A) The tables have a shared column, but their column names are not identical, so a join... ON is needed.
B) These two tables do not share any identical columns/fields.
C) The tables do not have a foreign key relationship.
D) The syntax used for natural join is not correct.

Answer 1

Answer: The query you provided attempts to perform a natural join between the "customer" and "employee" tables using the NATURAL JOIN clause. The NATURAL JOIN clause automatically joins tables based on columns with the same name. In your query, you have specified the same column name multiple times in the SELECT clause (i.e., "name").

Explanation: The query you provided attempts to perform a natural join between the "customer" and "employee" tables using the NATURAL JOIN clause. The NATURAL JOIN clause automatically joins tables based on columns with the same name. In your query, you have specified the same column name multiple times in the SELECT clause (i.e., "name").

The correct answer explaining why the query is not valid as a natural join is:

**A) The tables have a shared column, but their column names are not identical, so a join... ON is needed.**

Explanation: In a natural join, the join condition is based on columns with identical names. If the tables have columns with the same name but are not identical, a join using the ON clause is needed to explicitly specify the join condition.

Option B is incorrect because the tables in your query are attempting a natural join, which requires identical column names.

Option C is not necessarily a reason for the query to be invalid as a natural join. Foreign key relationships are not a requirement for a natural join.

Option D is not accurate; the syntax used for natural join is correct, but the issue lies in the attempt to select the same column multiple times with identical aliases.

Answer 2

The natural join is invalid because the tables do not share identical columns/fields. No table is inherently more correct, but natural join simplifies queries when suitable columns exist.

The Correct Option is; B) These two tables do not share any identical columns/fields.

Step-by-step explanation:

The query is not valid as a natural join because option B) These two tables do not share any identical columns/fields, is typically the correct answer if the natural join is not working.

A natural join requires that the two tables have at least one column with the same name and compatible data types. If there is no such column, then the database can't perform the join automatically, as it doesn't know on which column to base the join.

When you perform a natural join, the database management system automatically uses the columns with the same names in both tables to combine the data.

However, no table is more correct than the other inherently. The design should be dictated by the data model and the normalization requirements.

When you need to group data differently, you may consider using other types of joins, such as an inner join with a specified ON clause or another form of join that explicitly states the joining conditions. The advantages of grouping data using a natural join include reduced complexity in the query (not having to specify the joining conditions explicitly).

Switching between tables in the response is due to the evaluation of the requirements of the given query and the structure of the tables. If identical column names exist, a natural join is feasible, otherwise, it is not.