Natural JOIN operation

Owned by Computer Science Department
Last updated: Aug 01, 2023
2 min read

In SQL, a NATURAL JOIN is a type of join that automatically matches and combines rows from two tables based on columns with the same name and data type. It is a shorthand way of performing an INNER JOIN on columns that have matching names.

The basic syntax of the NATURAL JOIN is as follows:

SELECT column1, column2, ... FROM table1 NATURAL JOIN table2;

In this syntax, table1 and table2 are the two tables you want to join. The NATURAL JOIN automatically matches columns with the same name in both tables and combines rows where the values in those columns match.

Here's an example to illustrate the NATURAL JOIN:

Suppose we have two tables, "Customers" and "Orders," with columns as follows:

Customers table:

  • CustomerID

  • CustomerName

  • ContactEmail

Orders table:

  • OrderID

  • CustomerID

  • OrderDate

  • TotalAmount

If we want to retrieve the orders along with the customer name and contact email for each order, we can use the NATURAL JOIN:

SELECT OrderID, CustomerName, ContactEmail, OrderDate, TotalAmount FROM Customers NATURAL JOIN Orders;

In this example, the NATURAL JOIN matches the CustomerID column in both tables and combines the relevant rows from "Customers" and "Orders" where the CustomerID values match. This allows us to retrieve the desired information without explicitly specifying the join condition.

It's important to note that while the NATURAL JOIN can be convenient in some cases, it has some limitations and potential risks:

  1. Ambiguous Columns: If both tables have columns with the same name but different meanings, the NATURAL JOIN can lead to ambiguity in the result set.

  2. Lack of Control: The NATURAL JOIN does not allow you to specify the join condition explicitly, which can limit your control over the join operation.

  3. Performance: Depending on the size and structure of the tables, the NATURAL JOIN might not always be the most efficient way to perform the join.

Due to these limitations and potential risks, many SQL developers prefer to use explicit INNER JOIN or other types of joins with a specified join condition to have better control and understanding of the data merging process.

 

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