Which of the following is one of the basic approaches for joining tables?SubqueriesNatural joinUnion JoinDAll of the above

To determine which option is one of the basic approaches for joining tables, let's analyze the provided choices:

1. Subqueries: Subqueries can be used in SQL to retrieve data from one table based on a query in another table. While they can be related to joining tables, they are not a direct method of joining but rather a technique for retrieving data.

2. Natural join: A natural join is an SQL operation that automatically joins tables based on their common columns and eliminates duplicate columns from the result. This is indeed a basic approach for joining tables.

3. Union join: This term may be a bit misleading as "UNION" in SQL is used to combine the results of two or more SELECT statements. While it's related to working with tables, it's not specifically a joining operation like INNER JOIN or LEFT JOIN.

4. All of the above: This option suggests that all the previous methods are valid approaches for joining tables.

Considering the definitions and standard practices in SQL:

• The natural join is a direct method for joining tables.
• Subqueries and union operations are relevant but not basic table join methods.

Final Answer

Natural join is one of the basic approaches for joining tables. Therefore, the correct answer is: Natural join.