What's the Key Difference Between Natural JOIN and Inner JOIN in SQL?

Understanding the Distinction Between Natural Join and Inner Join

In the realm of SQL (Structured Query Language), it is essential to comprehend the differences between natural and inner joins. These join types are similar yet distinct, impacting the resulting data retrieval.

An inner join, denoted as INNER JOIN or USING, combines rows from two tables based on equality in one or more columns specified in the ON clause. In contrast, a natural join, represented by NATURAL JOIN, automatically joins tables based on columns that share the same name in both tables.

A key distinction lies in the number of columns returned. An inner join maintains all columns from both tables, while a natural join excludes duplicate columns with the same name. This occurs because the natural join assumes that the common columns contain the same data and are redundant.

For instance, consider two tables, TableA and TableB, with Column1 as the common column. An inner join would return all rows from both tables and include both instances of Column1:

SELECT * 
FROM TableA AS a 
INNER JOIN TableB AS b 
USING (Column1);

Output:

+------------+-----------+------------+-----------+
| a.Column1  | a.Column2 | b.Column1  | b.Column3 |
+------------+-----------+------------+-----------+
| 1          |  2        | 1          |   3       |
+------------+-----------+------------+-----------+

However, a natural join between TableA and TableB would omit the redundant Column1:

SELECT * 
FROM TableA 
NATURAL JOIN TableB;

Output:

+------------+----------+----------+
| Column1    | Column2  | Column3  |
+------------+----------+----------+
| 1          |  2       |   3      |
+------------+----------+----------+

It is crucial to note that in natural joins, the joining columns are implicitly determined by their shared names, and you cannot specify them explicitly. Additionally, natural joins can only be performed on tables with a single common column.

Understanding these nuances between inner joins and natural joins is essential for effective data retrieval. By choosing the appropriate join type, you can optimize your queries and obtain the desired results.

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