PostgreSQL – NATURAL JOIN

The NATURAL JOIN is a type of join that automatically matches columns with the same name in two or more tables and combines the rows where those columns have matching values. Essentially, a NATURAL JOIN performs an INNER JOIN using the columns with the same names as the join criteria.

The basic syntax of a NATURAL JOIN in PostgreSQL is as follows:

SELECT column_list FROM table1 NATURAL JOIN table2;

Here’s a breakdown of the components:

• SELECT column_list: This is the list of columns you want to retrieve from the combined result set.
• table1: The first table you want to perform a natural join with another table.
• table2: The second table you want to perform a natural join with the first table.

Example: Consider two tables: “employees” and “departments.” If both tables have a column named “department_id” and you want to find all employees in each department using a natural join, you can use the following query:

SELECT * FROM employees NATURAL JOIN departments;

In this example, the query performs a natural join using the “department_id” column that exists in both the “employees” and “departments” tables. The result will include only the columns from the two tables that are not involved in the join.

While NATURAL JOINs can simplify queries by automatically matching columns with the same names, they also have some potential pitfalls. For example, if the column names change in the future or if there are additional columns with the same name in the tables that you don’t intend to use for joining, the behavior of the query might not be as expected.

Due to the ambiguity and potential for unexpected results, many database professionals prefer using explicit JOIN conditions with the ON clause, specifying the exact columns to join on. This provides better control and avoids potential issues caused by column name changes or other changes in the schema.