How to Efficiently Retrieve Only the Most Recent Row in a MySQL JOIN with Pagination?

Retrieving the Most Recent Row Only in a MySQL JOIN with Pagination

When dealing with historical data tables like customer_data, it's often desirable to join only the most recent row to another table, while also managing pagination.

Original Query:

SELECT *, CONCAT(title,' ',forename,' ',surname) AS name
FROM customer c
INNER JOIN customer_data d on c.customer_id=d.customer_id
WHERE name LIKE '%Smith%' LIMIT 10, 20

Optimized JOIN with WHERE Clause:

To retrieve only the most recent row for each customer, add the following condition to the WHERE clause:

...
WHERE
  d.customer_data_id IN (
    SELECT MAX(customer_data_id)
    FROM customer_data
    WHERE customer_id = c.customer_id
  )
...

Alternative Indexing Solution:

For improved performance, especially in heavy queries, consider creating an index on the (customer_id, customer_data_id) columns in customer_data. This allows MySQL to quickly identify the most recent row for each customer.

Example WHERE Clause with Index:

...
WHERE
  d.customer_id = c.customer_id AND
  d.customer_data_id = (
    SELECT MAX(customer_data_id)
    FROM customer_data
    WHERE customer_id = c.customer_id
  )
...

CONCAT with LIKE:

Yes, using CONCAT with LIKE is a valid method for searching on multiple fields concatenated together. This is particularly useful when the original columns are not indexed and would normally result in a full table scan.

Additional Considerations:

• Pagination: The LIMIT and OFFSET clauses should be applied to the outer query (i.e., outside the subquery).
• JOIN Type: INNER JOIN is generally correct for retrieving all matching rows from both tables. However, you may want to experiment with other JOIN types to optimize performance based on your specific data structure.

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