How to Retrieve Only the Most Recent Row When Joining MySQL Tables?

Joining MySQL Tables to Retrieve Only the Most Recent Row

In data management systems, joining tables is essential to combine information from multiple sources. When dealing with historical data, it often becomes necessary to retrieve the most recent row from one of the joined tables.

Consider the scenario of a customer database where customer data is stored in two tables: customer and customer_data. The customer table contains basic customer information, while customer_data stores changes to the customer's profile. To display the customer's information in a table, the two tables need to be joined, but we only want the most recent row from customer_data.

To achieve this, you can utilize MySQL's MAX() function along with a subquery to find the ID of the most recent row in customer_data. The query would look something like this:

SELECT 
  c.*,
  cd.value
FROM 
  customer c
LEFT JOIN 
  customer_data cd ON c.customer_id = cd.customer_id
WHERE 
  cd.customer_id = (
    SELECT 
      MAX(customer_id) 
    FROM 
      customer_data
    WHERE 
      customer_id = c.customer_id
  )

This query first retrieves all the columns from the customer table (prefixed with c.). It then performs a LEFT JOIN with the customer_data table (prefixed with cd.), filtering the rows in customer_data to only include those with the maximum customer_id for each customer (as determined by the subquery).

Furthermore, as mentioned in the reference query, you can use CONCAT() with LIKE to search for specific values in concatenated columns. In the sample query, CONCAT(title,' ',forename,' ',surname) is being compared to the string '%Smith%'. This would return all customer names containing the substring "Smith" anywhere in the combined field.

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