PHP/SQL Update - update only if value has been change

Bobby tables will destroy your database. All your bits are belong to him (strictly speaking, this is an exaggeration, but you need to wrap all of your db inputs with mysql_real_escape_string or better yet, move to PDO's or MySQLi).

Long and the short? No, there is no reliable way to determine whether user input is the same as what is in the database without actually querying the database first or somehow storing the original output from the DB locally ($_SESSION or whatnot).

There are legitimate use cases for that, but it looks like you're better off just calling the updates. You can prevent them slightly by adding AND LIVE != '$live' AND UR2 != '$ur2', but you'll still need to run that many queries.

BTW -- I generally advise people not to use traditional for loops in PHP pretty much ever. PHP's foreach is better in almost every way. Instead of for ($i=0;$i<count();$i++), use foreach( $_POST['id'] as $i => $id ). You'll already have $id declared.

Actually, I think that a good way of doing is to:

1) Perform a query to get the old record from the db, then store the row contents in an associative array, with column names as keys.

2) Create a new array by checking the content of each "column" to be updated. If the content received is different from the value stored on the db, update the record data, else ignore and go ahead. Finally send back the updated data to the db with an UPDATE

function updateRecord(array $input_data) {

   // Get the data associated to the record id we want to update.
   $record_data = $yourDBWrapperClass
                     ->where("id",$_GET['record_id'])
                     ->get(TABLE_NAME);  

   // Process column by column and append data to the final array.

   $final_data = [];
   $ignored_columns = ['id', 'last_update'];

   foreach ($record_data as $col_name => $value) {

       // Update the record data, only when input data shows a difference
       if(array_key_exists($col_name, $input_data) 
           && 
          $record_data[$col_name] != $input_data[$col_name]) 
       {
          $final_data[$col_name] = $inputData[$col_name];
       }
       else if (array_key_exist($ignored_columns, $col_name) == FALSE && $record_data[$col_name] == $input_data[$col_name] 
       {
          $final_data[$col_name] == $value;
       }

   }


  // Finally, perform the db update.

  $update_result = $yourDBWrapperClass
                       ->where("id", $_GET['record_id'])
                       ->update(TABLE_NAME, $final_data);


  return $update_result ? "Record update success" : "Record update failed";

}

note: You don't need to send back the id, or last_update columns: their value is calculated automatically by the server. Sending a wrong value, will cause an error, or provide a wrong information. Think about the last_update column: it's better to leave to MySQL, which will call use the column default to get the value: NOW(); or CURDATE();

expected aspect of variables/arrays

$_GET['record_id'] = 123;

$record_data = [
   "id" => 123,
   "name" => "John",
   "surname" => "Dahlback",
   "age" => 31,
   "last_update" => "2019-01-01 10:00:00"
];

$input_data = [
   "age" => 32
];

$final_data = [
  // "id" => 123,
  "name" => "John",
  "surname" => "Dahlback",
  "age" => 32,
  // "last_update" => CURDATE();
];