All About Natural Joins in SQL
A Natural Join is an operation that creates an implicit join clause for you based on the common columns in the two tables being joined. This article will teach us how to use natural join in sql.
In the previous blogs, we briefly discussed different joins in SQL, like inner join, left join, right join, and full outer join. In this article, we will explore another join in SQL, i.e., Natural Join in SQL.
Natural join is an inner join that automatically joins two or more tables on all columns with the same name and data type. But both inner join and natural join are different.
In this article, we will explore natural joins more with the help of different examples, and at the end of the article, we will see the difference between natural join and inner join.
So, let’s start the article with the definition of Natural Join.
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What is Natural Join in SQL?
A natural join in SQL is a type of join operation that combines rows from two or more tables based on their common columns. The join is performed by comparing the values in the columns with the same name in both tables and combining the rows with matching values into a single result set. The columns with the same name in both tables must have the same data type and size.
Dissimilar to other joins, it doesn’t require any explicit condition for joining. Instead, it relies on the inherent structure of the tables.
Syntax of Natural Join
SELECT * FROM table1 NATURAL JOIN table2;
Let’s take an example to better understand Natural Join in SQL.
Let us have two tables of customers and orders:
customer
| customer_id | Name | |
| 1 | ramesh | ramesh@gmail.com |
| 2 | suresh | suresh@gmail.com |
orders
| order_id | customer_id | product_id | quantity |
| 1 | 1 | 100 | 2 |
| 2 | 2 | 200 | 1 |
Problem Statement: Return a table that contains all the columns from both the customer and orders, with only one copy of each column.
SELECT *FROM customersNATURAL JOIN orders;
Output
| customer_id | name | product_id | quantity | |
| 1 | ramesh | ramesh@gmail.com | 100 | 2 |
| 2 | suresh | suresh@gmail.com | 200 | 1 |
When to use Natural Join in SQL?
You can use Natural Join in SQL when:
- Tables have columns with matching names intended to represent the same data.
- You have an assurance that the schema won’t change, introducing unexpected columns.
- There’s clarity in data design, and ambiguity is minimal.
Implementing Natural Join in SQL
Problem Statement: Let we have two tables Students (student_id, student_name, and major_id) and Majors (major_id and major_name). Write an SQL query to fetch the student_name and major_name.
Student Table
| student_id | student_name | major_id |
|---|---|---|
| 1 | Alice Smith | 101 |
| 2 | Bob Johnson | 102 |
| 3 | Charlie Brown | 103 |
| 4 | David Jones | 104 |
| 5 | Evelyn White | 101 |
| 6 | Frank Harris | 105 |
| 7 | Grace Green | 102 |
| 8 | Harry Clark | 103 |
| 9 | Isabella Lewis | 104 |
| 10 | Jack King | 105 |
Majors Table
| major_id | major_name |
|---|---|
| 101 | Computer Science |
| 102 | Biology |
| 103 | Mechanical Engineering |
| 104 | Arts and Humanities |
| 105 | Business Administration |
SQL Query using in Natural Join
SELECT student_name, major_nameFROM StudentsNATURAL JOIN Majors;
Output
| student_name | major_name |
|---|---|
| Alice Smith | Computer Science |
| Bob Johnson | Biology |
| Charlie Brown | Mechanical Engineering |
| David Jones | Arts and Humanities |
| Evelyn White | Computer Science |
| Frank Harris | Business Administration |
| Grace Green | Biology |
| Harry Clark | Mechanical Engineering |
| Isabella Lewis | Arts and Humanities |
| Jack King | Business Administration |
Now, let’s see how to fetch the same result using inner join in sql.
SELECT student_name, major_nameFROM StudentsINNER JOIN Majors ON Students.major_id = Majors.major_id;
The above query will produce the same result. But the question is how these two queries are different from each other.
- Explicitness: With INNER JOIN, you specify which columns to join. This makes it clear to anyone reading the query what the joining condition is and can prevent potential issues if the schema changes.
- Safety: If, in the future, a new column with the same name but a different meaning is added to both tables, a NATURAL JOIN might produce incorrect results because it will try to join on that new column as well. With INNER JOIN, you’re safeguarded against such inadvertent changes.
- Flexibility: INNER JOIN offers greater flexibility because you can join tables on columns with different names or even on more complex conditions.
Difference Between Natural Join and Inner Join
Natural join is a simpler and more concise way to combine data from multiple tables. Still, it is limited to tables with common columns and matching names and data types. An inner join allows you to specify any columns as the join condition but requires writing a more complex join clause. Here is a detailed difference between the two.
| Natural Join | Inner Join | |
| Definition | A join that combines rows from two or more tables based on their common columns | A join that combines rows from two or more tables based on a specified join condition |
| Syntax | SELECT * FROM table1 NATURAL JOIN table2 | SELECT * FROM table1 INNER JOIN table2 ON table1.column = table2.column |
| Use of common columns | Automatically uses common columns with matching names and data types as the join condition | Allows you to specify any columns as the join condition |
| Result set | Includes all columns from both tables and only rows where common columns have matching values | Includes columns from both tables and only rows that satisfy the join condition |
Advantages and Disadvantages of Natural Join in SQL
| Advantages | Disadvantages |
| Provides a shorthand way to join tables without specifying columns. | The simplicity can be deceptive. A lack of explicitness can make it easier to understand the join condition if you know the table schema. |
| Useful for quick ad-hoc queries or data exploration. | Heavily relies on the database schema being consistent. |
| It is useful when tables have columns with the same names and meanings | May require more maintenance as the database evolves. Changes in one table might necessitate changes in related SQL queries. |
| Can join tables on multiple columns without explicitly listing them, provided column names match. | It is not suitable for situations where related columns have different names. |
Conclusion
In conclusion, natural joins can be a useful tool for quickly combining data from multiple tables without specifying the join conditions explicitly. However, they can produce unexpected results if the tables to be joined have columns with the same name but different meanings or data types.
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FAQs
What is a Natural Join in SQL?
A Natural Join in SQL is a type of join that combines rows from two or more tables based on their related columns. This type of join uses the common columns with the same name in both tables to match rows.
How does Natural Join differ from other types of joins in SQL?
Natural Join differs from other types of joins in that it automatically matches rows based on the common columns with the same name and data type in both tables. There is no need to explicitly specify the condition for the join as in other types of joins.
Does a Natural Join eliminate duplicate columns?
Yes, a Natural Join eliminates duplicate columns in the result set. It returns each pair of columns (from Table1 and Table2) that have the same name only once, using the values where the join condition is true.
What happens if there are no common columns between the tables in a Natural Join?
If there are no common columns between the two tables, a Natural Join will result in a Cartesian product, i.e., it will return all combinations of rows from both tables, which can be a very large set of results and not usually what you want.
Vikram has a Postgraduate degree in Applied Mathematics, with a keen interest in Data Science and Machine Learning. He has experience of 2+ years in content creation in Mathematics, Statistics, Data Science, and Mac... Read Full Bio
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