How to Efficiently Find the Most Recent Position for Each Security in a Database?

Groupwise Maximum

You are trying to retrieve the most recent position for each security from a given table. To achieve this, you can use the following query:

SELECT p1.id, 
       p1.security, 
       p1.buy_date 
       FROM positions p1
LEFT JOIN
            positions p2
                ON p1.security = p2.security
                   AND p1.buy_date < p2.buy_date
      WHERE 
      p2.id IS NULL;

In this query, the left join is used to compare each row in the positions table to every other row with the same security. The buy_date column is used to determine which row is the most recent. The WHERE clause then filters out any rows that are not the most recent for their respective security.

The result of this query will be a table with one row for each security, containing the most recent id, security, and buy_date for that security.

This query is more efficient than the subquery-based approach you previously tried because it does not require multiple passes through the positions table. Instead, it uses a single join to identify the most recent row for each security, making it significantly faster for large datasets.

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