An outer join is a type of join operation in relational database management where all records from one table are retrieved, and the matching records from the second table are included. If there is no matching record in the second table, it will still retrieve the record from the first table, but with null values for the fields that were not matched.
For example, if you have a customer table and an order table, an outer join would retrieve all the customers from the customer table regardless of whether they have placed an order or not. It would also include the order information for those customers who have placed an order, and null values for those who have not.
An inner join, on the other hand, only retrieves records where there is a match in both tables based on a specified criterion.
FAQs
Why would you use an outer join?
An outer join can be useful when you want to include all records from one table, even if there are no matches in the other table. This can be helpful for generating reports or analysis where you need to see all data, regardless of whether some of it is missing.
What are null values?
Null values are fields in a table that have no value or an unknown value. They are often used in outer joins to indicate when there is no matching record in the second table.
Conclusion
An outer join is a useful tool in relational database management for retrieving all records from one table and matching records from a second table. It allows for the inclusion of null values for unmatched fields and can be helpful in generating comprehensive reports or analysis of data.
