In what scenarios should PHP developers consider restructuring their queries to avoid using MySQL variables for better performance and reliability?

When dealing with large datasets or complex queries, PHP developers should consider restructuring their queries to avoid using MySQL variables for better performance and reliability. Using MySQL variables can lead to slower query execution times and potential issues with scalability. Instead, developers can achieve the same results using JOINs, subqueries, or temporary tables.

// Example of restructuring a query to avoid using MySQL variables
$query = "SELECT t1.id, t1.name, t2.total_sales
          FROM table1 t1
          JOIN (
              SELECT id, SUM(sales) as total_sales
              FROM table2
              GROUP BY id
          ) t2 ON t1.id = t2.id";

$result = mysqli_query($connection, $query);

// Process the query result
while ($row = mysqli_fetch_assoc($result)) {
    // Handle each row as needed
}