What are the key differences between natural joins and inner joins in relational databases?

Comparing Natural Join and Inner Join Operations

Natural join and inner join are two common types of joins used in relational database management systems. They share the characteristic of combining rows from multiple tables based on shared column values, but they differ in the treatment of repeated columns and the specification of joining criteria.

Natural Join

A natural join is a simplified form of inner join that automatically selects common columns between the tables being joined. Instead of specifying the joining columns explicitly, as with inner join, natural join identifies and joins tables based on column names that are identical in both tables.

Inner Join

In contrast, an inner join requires the user to specify the joining columns by utilizing the ON or USING clauses. The ON clause compares columns from different tables, while the USING clause identifies common columns between the tables.

Differences in Resulting Columns

One of the key differences between natural join and inner join is the number of columns returned in the result. Natural join excludes repeated columns from the result, while inner join retains all columns from both tables.

Example

Consider the following two tables:

TableA:
+------------+----------+
| Column1     | Column2  |
+-----------------------+
| 1          |  2       |
+------------+----------+

TableB:
+--------------------+
| Column1  |  Column3 |
+--------------------+
| 1       |   3      |
+---------+----------+

If we perform an inner join on Column1, the result would include all columns from both tables:

INNER JOIN TableA AS a ON a.Column1 = b.Column1
+------------+-----------+----------+----------+
| a.Column1  | a.Column2 | b.Column1| b.Column3|
+------------------------+-----------+----------+----------+
| 1          |  2        | 1        |   3      |
+------------+-----------+----------+----------+

On the other hand, a natural join on Column1 would only include the unique columns, removing the duplicate Column1 column:

NATURAL JOIN TableA
+------------+----------+----------+
| Column1     | Column2  | Column3  |
+-----------------------+----------+
| 1          |  2       |   3      |
+------------+----------+----------+

Conclusion

While both natural and inner joins serve the purpose of combining rows from multiple tables, they have distinct differences in terms of column handling and the method of specifying joining criteria. Understanding these differences is essential for effective database joins and data retrieval in various applications.

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