Full outer join

Definition

A full outer join is a type of SQL join that returns all records from both tables involved in the query, even if there are no matches between them. It combines the results of both left and right outer joins, ensuring that all rows from both tables are included in the final result set. This is particularly useful for comparing datasets or identifying discrepancies across two tables.

5 Must Know Facts For Your Next Test

1. A full outer join will return rows where there are matches in either table as well as rows where there are no matches, providing a complete view of both datasets.
2. In a full outer join, when a row from one table does not match any rows from the other table, the result will show null values for the columns of the non-matching table.
3. Full outer joins can lead to larger result sets compared to inner or left/right joins because they include all records, regardless of matches.
4. To execute a full outer join in SQL, you use the syntax `SELECT * FROM table1 FULL OUTER JOIN table2 ON condition`.
5. Full outer joins are particularly useful in data analysis for identifying gaps or discrepancies between two related datasets, allowing for comprehensive insights.

Review Questions

• How does a full outer join differ from an inner join and what implications does this have for data retrieval?
  • A full outer join differs from an inner join in that it includes all records from both tables, regardless of whether there are matches. While an inner join only retrieves rows with matching values in both tables, a full outer join provides a more comprehensive dataset that includes unmatched rows. This difference is crucial when analyzing data where completeness is important, as it allows for better insights into relationships and gaps between datasets.
• Discuss how a full outer join can be beneficial in comparing two datasets with potential discrepancies.
  • A full outer join is beneficial for comparing two datasets because it ensures that all records from both datasets are represented in the result set. This allows analysts to easily identify discrepancies and missing data points by showing null values where matches do not exist. By examining these unmatched records, one can understand the extent of differences between the datasets and take corrective action if necessary.
• Evaluate a scenario where using a full outer join would be more appropriate than using a left or right outer join, and explain your reasoning.
  • Consider a scenario where you have two tables: one containing customer orders and another containing customer feedback. If you want to analyze all orders alongside any feedback received, using a full outer join would be appropriate because it would display all orders regardless of whether feedback was provided, and also show any feedback that does not correspond to an order. This comprehensive view helps assess customer satisfaction more effectively than just focusing on matched pairs through left or right joins.

Related terms

inner join: An inner join retrieves only the records that have matching values in both tables, excluding any non-matching rows.

left outer join: A left outer join returns all records from the left table and the matched records from the right table, filling in nulls for non-matching rows on the right.

right outer join: A right outer join returns all records from the right table and the matched records from the left table, filling in nulls for non-matching rows on the left.