Full Join
Introduction
Full join is a type of join operation in SQL that combines rows from two or more tables based on a related column between them. Unlike other join operations such as inner join or left join, full join includes all rows from both tables, even if there is no match between the columns being joined.
How Full Join Works
In a full join, the result set includes all rows from both tables. If a match is found based on the join condition, the result set will include that row from the first table along with the matching row from the second table. If there is no match, the result set will include the row from the first table with NULL values for the columns of the second table, and vice versa.
Example:
Let's consider two tables: \"Customers\" and \"Orders\". The \"Customers\" table contains information about customers, while the \"Orders\" table contains information about the orders placed by those customers. We want to get a list of all customers and their corresponding orders.
The \"Customers\" table:
| CustomerID | CustomerName |
|---|---|
| 1 | John Doe |
| 2 | Jane Smith |
| 3 | Robert Johnson |
The \"Orders\" table:
| OrderID | CustomerID | OrderDate |
|---|---|---|
| 1 | 1 | 2021-01-01 |
| 2 | 2 | 2021-01-02 |
The full join query:
SELECT Customers.CustomerID, Customers.CustomerName, Orders.OrderID, Orders.OrderDate
FROM Customers
FULL JOIN Orders
ON Customers.CustomerID = Orders.CustomerID;
The query will return the following result:
| CustomerID | CustomerName | OrderID | OrderDate |
|---|---|---|---|
| 1 | John Doe | 1 | 2021-01-01 |
| 2 | Jane Smith | 2 | 2021-01-02 |
| 3 | Robert Johnson | NULL | NULL |
As shown in the result, the full join includes all rows from both tables. The first two rows are the matched rows based on the common CustomerID column, while the third row is from the \"Customers\" table but not found in the \"Orders\" table, hence displaying NULL values for the columns of the \"Orders\" table.
Use Cases
Full join is useful when you want to include all rows from both tables, regardless of whether there is a match between the joining columns. It is commonly used in scenarios where you want to analyze data that may not have a complete match or when you need a complete overview of the data from both tables.
For example, in the above example, the full join allows us to see all customers and their corresponding orders, even if a customer has not placed any orders yet. This can be helpful in analyzing customer behavior, identifying potential gaps in sales, or conducting comprehensive reporting.
Conclusion
Full join is a powerful tool in SQL that combines rows from two or more tables, including all rows from both tables regardless of a match. It provides a complete overview of the data and can be useful in various scenarios where a complete set of data from multiple tables is required. Understanding how full join works and its potential use cases is essential for SQL developers and analysts.
