How Can I Optimize Groupwise Maximum Queries Without Full Table Scans?

Optimizing Groupwise Maximum Queries without Full Table Scans

The inefficiency of the query you provided is due to the full table scan performed to retrieve maximum IDs for each option_id. Below are strategies to optimize this query without such scans:

Utilizing a Separate Table:

Create a separate table, such as "options," that stores option_ids along with their corresponding maximum IDs. Establish a foreign key relationship between records and options to ensure integrity. This allows for efficient querying of maximum IDs by joining records on option_id.

Correlated Subqueries with an Index:

Using a correlated subquery referencing an index on (option_id, id) can efficiently retrieve the maximum ID for each option_id. The subquery will only access the relevant rows, eliminating the need for a full table scan.

Lateral Joins:

In PostgreSQL 9.3 and later, lateral joins can be used in conjunction with a CTE to simulate index-only scans by joining on a lateral subquery that fetches the desired values from an index.

MySQL Optimization:

Interestingly, MySQL 5.5 can optimize this query using an index on records(option_id, id). This suggests that MySQL has a mechanism for optimizing groupwise maximum queries with specific index structures.

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