How to Efficiently Retrieve the Most Recent Location Data for Each Record in a Joined Statement?

Selecting the Most Recent Date in a Joined Statement: Troubleshooting for Historic Location Data retrieval

This query aims to retrieve a record's historic locations and their corresponding dates. However, the current implementation takes an excessively long time to execute and produces duplicate records. The expected output is a simplified list of records with their most recent locations.

The original query attempts to find the most recent date associated with each record id by executing a self-join operation. However, this approach is inefficient and can lead to performance issues, especially for larger datasets.

Correct Query

To optimize the query, we can utilize the following corrected version:

SELECT t1.received_id
     , t1.transaction_id
     , t1.date_modified
     , l.location
  FROM transactions t1
  JOIN ( SELECT received_id, MAX(date_modified) maxmodify FROM transactions GROUP BY received_id) max_record
    ON max_record.received_id = t1.received_id 
   AND max_record.maxmodify = t1.date_modified
  JOIN locations l
    ON l.location_id = t1.location_id
  JOIN received r
    ON r.received_id = t1.received_id
 WHERE t1.received_id = '1782'
 ORDER 
    BY t1.date_modified DESC

Explanation

In this query, we introduce a common table expression (CTE) to find the max date for each record id in the transactions table. The CTE is:

SELECT received_id, MAX(date_modified) AS maxmodify
FROM transactions
GROUP BY received_id

We then join the original transactions table (t1) with this CTE (max_record) on the received_id field. Additionally, we filter on the maxmodify column to ensure that only transactions with the most recent date are included. This optimizes the query by avoiding unnecessary joins and duplicates.

With this optimized query, we can effectively obtain the historic locations for each record, ensuring that we retrieve only the most recent location for each unique record id.

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