Updating Recently Updated Row by ID in PrestaShop Database

In this article, we’ll explore a challenging problem related to updating product attributes in a PrestaShop database. The goal is to update only recently updated rows for specific product IDs when their quantity is zero. We’ll delve into the solution provided by the Stack Overflow community and provide an in-depth explanation of the approach.

Problem Statement

The question arises from trying to update default product attribute values in a PrestaShop database. The issue at hand is to ensure that only one row for a specific id_product ID is updated when its quantity reaches zero. Additionally, we want to avoid updating the default_on value if there are multiple rows with the same id_product ID and quantity equals zero.

Initial Attempt

The initial attempt provided in the Stack Overflow question attempts to update both rows simultaneously using a single transaction:

START TRANSACTION;
SET @update_id := 0;
UPDATE ps_product_attribute SET default_on = NULL, id_product = (SELECT @update_id := id_product)
WHERE `default_on` = 1 AND `quantity` = 0
LIMIT 1;

UPDATE ps_product_attribute SET default_on = 1
WHERE `id_product` = @update_id AND `quantity` > 0 AND `default_on` IS NULL
LIMIT 1;
COMMIT;

This approach has several drawbacks:

• It can update multiple rows if there are multiple matching results for the same id_product ID and quantity equals zero.
• The second UPDATE statement is unnecessary, as the initial UPDATE statement already updates the row with the smallest id_product.

Solution

The Stack Overflow community suggested using a self-join to identify unique rows for each id_product. Here’s an improved solution:

UPDATE ps_product_attribute AS t1
JOIN (
    SELECT id_product
    FROM ps_product_attribute
    GROUP BY id_product
    HAVING COUNT(*) > 1
) AS t2 ON t1.id_product = t2.id_product
SET default_on = CASE
    WHEN default_on = 1 AND quantity = 0 THEN NULL
    WHEN quantity > 0 AND default_on IS NULL THEN 1
    ELSE default_on -- leave the rest unchanged
END;

This solution works as follows:

• It identifies unique rows for each id_product ID by joining ps_product_attribute with a subquery that groups results by id_product and filters out those with only one matching result.
• The main update statement then uses this self-join to set the default_on value based on conditions similar to the initial attempt.

Understanding the Self-Join Approach

The key to understanding this solution lies in recognizing how SQL handles grouping and joining data:

• When you group results by a column (GROUP BY id_product), the resulting subquery contains all rows that share the same id_product value.
• By using a self-join (JOIN t1 ON t1.id_product = t2.id_product), we can combine this subquery with the original table to identify unique rows.

Performance Considerations

This solution has a few advantages over the initial attempt:

• It uses only one UPDATE statement, reducing the overhead of transaction management and limiting concurrency issues.
• By joining the table with a self-join, we can avoid unnecessary subqueries or correlated subqueries.

However, it’s essential to consider potential performance implications when dealing with large datasets. In some cases, using a self-join might lead to increased processing time due to additional joins and grouping operations.

Conclusion

The solution provided in the Stack Overflow community example offers a practical approach to updating recently updated rows for specific product IDs in PrestaShop database. By leveraging self-joins and conditional updates, we can efficiently manage complex logic while avoiding unnecessary iterations or concurrency issues.

Last modified on 2025-03-12