PHP process MySQL query row-by-row - php

Question

I have combined a PHP script to count words in MySQL textfield and update another field accordingly.
It works well with relatively small tables - but when I tried with really big table (10M records) - of course I've got "PHP Fatal error: Allowed memory size of 134217728 bytes exhausted"
Could somebody hint how to modify the script below to process the data "row-by-row" ?
<?php
$con1 = mysqli_connect('localhost','USERNAME','PASSWORD','DATABASE');
if (!$con1) {
die('Could not connect: ' . mysqli_error($con1));
}
$sql = "SELECT id FROM TableName";
$result = mysqli_query($con1, $sql);
while ($row = mysqli_fetch_assoc($result)) {
$to = $row["id"];
$sql1 = "SELECT textfield FROM TableName WHERE id = '$to' ";
$result1 = mysqli_query($con1,$sql1);
$row1 = mysqli_fetch_assoc($result1);
$words=(str_word_count($row1['textfield'],0));
$sql2="UPDATE TableName SET wordcount = '$words' WHERE id ='$to'";
$result2 = mysqli_query($con1,$sql2);
}
mysqli_close($con1);
?>

Answer 1

MySQL queries have the clause limit o, n, so you can run
SELECT id FROM TableName limit 0, 10
for example to get only 10 elements from the start. Now, the first number is the offset (the index where you start your work from) and the second is the number of elements you would expect to get. Now, these are the ideas you need to know in order to have success in doing this:
you will need to write a loop
in the loop you will always get n elements (n could be 1 as you wanted, or more)
in each step you increment o by n, so the new offset will be starting where the results ended previously
you can ensure an order, like order by id, for example
you can wrap the loop we are speaking about here around most of your code