How can the PHP code be optimized to efficiently count the number of entries in column 3 that do not have corresponding values in columns 4 and 5?

To efficiently count the number of entries in column 3 that do not have corresponding values in columns 4 and 5, we can use a SQL query to filter out the rows where columns 4 and 5 are not empty or null. This can be achieved by using a SELECT query with a WHERE clause that checks for null or empty values in columns 4 and 5. Finally, we can use the mysqli_num_rows function to count the number of rows returned by the query.

<?php
// Assuming $conn is the mysqli connection object

$query = "SELECT COUNT(*) FROM table_name WHERE column3 IS NOT NULL AND (column4 IS NULL OR column4 = '') AND (column5 IS NULL OR column5 = '')";
$result = mysqli_query($conn, $query);

if ($result) {
  $row = mysqli_fetch_array($result);
  $count = $row[0];
  echo "Number of entries in column 3 without corresponding values in columns 4 and 5: " . $count;
} else {
  echo "Error executing query: " . mysqli_error($conn);
}

mysqli_close($conn);
?>