In SQL, a full join is a type of join operation used to combine records from two tables. It returns all the rows from both the tables, including the unmatched ones, and matches the rows where the specified condition is met. In this blog post, we will explore how the full join works and provide examples to better understand its usage.
Syntax
The syntax for a full join in SQL is as follows:
SELECT column_name(s)
FROM table1
FULL JOIN table2 ON table1.column_name = table2.column_name;
Example
Let’s consider two tables, Customers and Orders, with the following structure:
Customers Table
| CustomerID | CustomerName |
|---|---|
| 1 | John |
| 2 | Jane |
| 3 | Bob |
Orders Table
| OrderID | OrderDate | CustomerID |
|---|---|---|
| 1 | 2022-01-01 | 1 |
| 2 | 2022-02-01 | 2 |
| 3 | 2022-03-01 | 3 |
| 4 | 2022-04-01 | 4 |
To perform a full join on the Customers and Orders table, the following SQL query can be used:
SELECT Customers.CustomerName, Orders.OrderDate
FROM Customers
FULL JOIN Orders ON Customers.CustomerID = Orders.CustomerID;
This query will return the following result:
| CustomerName | OrderDate |
|---|---|
| John | 2022-01-01 |
| Jane | 2022-02-01 |
| Bob | 2022-03-01 |
| NULL | 2022-04-01 |
As you can see, the full join returns all the rows from both tables. The matching rows are displayed as expected, while the unmatched rows are filled with NULL values.
Use Cases
The full join can be helpful in various scenarios, including:
- Merging data from two tables: When you need to combine data from two tables, regardless of whether they have matching records or not, a full join provides a way to get all the data in one result.
- Finding unmatched records: By utilizing a full join, you can identify the unmatched records from each table by looking for
NULLvalues in the corresponding columns.
Conclusion
The full join in SQL is a powerful tool that enables you to combine data from two tables, including unmatched records. Understanding how to use the full join syntax and real-life use cases can help you manipulate and analyze data more efficiently. Experiment with the examples provided to solidify your understanding and explore further possibilities with the full join operation.
#SQL #Join