How to Efficiently Find Records with the Highest or Lowest Value Per Group Using a Left Outer Join?

Get Records with Highest/Smallest Value Per Group Using Efficient Join

While using ranks to find records with the highest or smallest value per group is possible, a more efficient and straightforward approach is to utilize a left outer join.

Example for Highest Value:

To retrieve the record with the highest OrderField per group, follow these steps:

1. Join the Table with itself on the condition that the target record's OrderField is lower than the outer record's OrderField:

SELECT t1.*
FROM `Table` AS t1
LEFT OUTER JOIN `Table` AS t2
  ON t1.GroupId = t2.GroupId AND t1.OrderField < t2.OrderField

2. Check for null values in the joined columns. If the join returns null, it means there is no record with a higher OrderField, indicating that t1 has the highest value.

Additional Considerations:

• If multiple records have the same highest OrderField, the query will return all of them. To ensure a single record is returned, further conditions can be added.
• Proper indexing on the GroupId and OrderField columns is crucial for optimal performance.

Avoidance of Ranks and Subqueries:

Using a left outer join eliminates the need for ranks and subqueries, leading to improved performance. As demonstrated earlier, the join method significantly outperforms subquery-based approaches.

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