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Introduction
Data in relational databases is often distributed among several tables. To gather coherent information from these tables, we need to join them. One way to do this is by using the SQL "Natural Join."
In this article, we will explore what a Natural Join is, how it functions, and where it fits in our SQL toolbox.
Understanding Natural Join in SQL
What is a Natural Join?
A Natural Join in SQL is a type of join that creates a new table by combining rows from two tables where the values of all matching columns are equal.
Why Use Natural Join?
Natural Join is beneficial when you need to:
Simplify Queries: It eliminates the need to specify a condition to match the records.
Reduce Errors: It automatically matches columns with the same name, reducing human error.
Improve Readability: It simplifies SQL code, making it more readable.
The Syntax of Natural Join
The syntax of Natural Join is:
SELECT columns
FROM table1
NATURAL JOIN table2;
Here, the tables table1 and table2 should have at least one common column.
Implementing Natural Join in Real Scenarios
Let's look at some examples of Natural Join.
Example 1: Basic Usage
Suppose we have two tables, 'Students' and 'Grades', both having a common column 'StudentID'. We want to get a complete list of students along with their grades.
Let’s see the students table:
Let’s now see the grades table:
We can use Natural Join as follows:
SELECT *
FROM Students
NATURAL JOIN Grades;
Output
Example 2: Multiple Natural Joins
We can also combine more than two tables using multiple Natural Joins. Suppose we now have another table, 'Courses', which also has a 'StudentID' column. We can join all three tables like this:
SELECT *
FROM Students
NATURAL JOIN Grades
NATURAL JOIN Courses;
Output
Types of Natural Join in SQL
There are two types of natural joins:
1. INNER NATURAL JOIN: It returns only the rows with matching values in both tables. For example,
SELECT employees.employee_id, employees.employee_name, departments.department_name
FROM employees
INNER JOIN departments ON employees.department_id = departments.department_id;
2. OUTER NATURAL JOIN: It returns all rows from both tables, with matching rows from the common columns and NULLs in columns where there is no match. For example,
SELECT employees.employee_id, employees.employee_name, departments.department_name
FROM employees
LEFT JOIN departments ON employees.department_id = departments.department_id;
Difference Between Natural and Inner Join in SQL
Aspect
Natural Join
Inner Join
Common Columns
Uses all columns with the same name and data type.
Requires explicit specification of columns for joining.
Syntax
Uses the "NATURAL JOIN" keyword.
Uses the "INNER JOIN" keyword, specifying join conditions.
Control over Join
Limited control, as it automatically selects columns.
Provides explicit control over columns and join conditions.
Readability
Offers simplicity and brevity in the query.
Requires more explicit syntax but offers greater customization.
Example
SELECT * FROM table1 NATURAL JOIN table2;
SELECT * FROM table1 INNER JOIN table2 ON table1.id = table2.id;
Frequently Asked Questions
What is the natural join in SQL?
A natural join in SQL combines tables based on common columns with the same name and data type, automatically matching these columns.
What is a natural join of a table with itself?
A self-natural join in SQL involves combining rows from the same table based on common column values, typically used for hierarchical data.
Is natural join a type of equi join?
Yes, a natural join is a type of equi join where the condition for matching rows is based on equality between common columns with the same name.
Conclusion
The Natural Join is a powerful tool in SQL that allows for effective data manipulation and retrieval. It simplifies complex SQL queries, reduces errors, and makes your code more readable. However, it's important to understand when to use it, as incorrect usage can lead to unintended results. Always ensure your tables have common columns with matching data types when using a Natural Join. By mastering SQL's various joining methods, including Natural Join, you can navigate your database with ease and efficiency.
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