PHP MySQL UPDATE query with array and IN statement - php

Question

I have this query which works successfully in one of my PHP scripts:
$sql = "UPDATE Units SET move_end = $currentTime, map_ID = $mapID, attacking = $attackStartTime, unit_ID_affected = $enemy, updated = now() WHERE unit_ID IN ($attackingUnits);";
$attackingUnits is an imploded array of anywhere between 1 - 100 integers.
What I'd like to do is also add arrays with different values for $currentTime and $mapID which correspond with the values for $attackingUnits. Something like this:
$sql = "UPDATE Units SET move_end = " . $attackingUnits['move_end'] . ", map_ID = " . $attackingUnits['map_ID'] . ", attacking = $attackStartTime, unit_ID_affected = $enemy, updated = now() WHERE unit_ID IN ($attackingUnits);";
Obviously that won't work the way I want it to because $attackingUnits['move_end'] and $attackingUnits['map_ID'] are just single values, not an array, but I'm stumped as to how I can write this query. I know I can one query for each element of $attackingUnits, but this is precisely what I'm trying to avoid as I'd like to be able to use one UPDATE for as many elements as required.
How would I write this query?
The key parts of the PHP script are:
$attackStartTime = time(); // the time the units started attacking the enemy (i.e. the current time)
// create a proper multi-dimensional array as the client only sends a string of comma-delimited unitID values
$data = array();
// add the enemy unit ID to the start of the selectedUnits CSV and call it allUnits. we then run the same query for all units in the selectedUnits array. this avoids two separate queries for pretty much the same columns
$allUnits = $enemy . "," . $selectedUnits;
// get the current enemy and unit data from the database
$sql = "SELECT user_ID, unit_ID, type, map_ID, moving, move_end, destination, attacking, unit_ID_affected, current_health FROM Units WHERE unit_ID IN ($allUnits);";
$result = mysqli_query($conn, $sql);
// convert the CSV strings to arrays for processing in this script
$selectedUnits = explode(',', $selectedUnits);
$allUnits = explode(',', $allUnits);
while ($row = mysqli_fetch_assoc($result)) {
$data[] = $row;
}
$result -> close();
$increment = 0; // set an increment value outside of the foreach loop so that we can use the pointer value at each loop
// check each selected unit to see if it can validly attack the enemy unit, otherwise remove them from selected units and send an error back for that specific unit
foreach ($data as &$unit) {
// do a whole bunch of checking stuff here
}
// convert the attacking units (i.e. the unit ids from selected units which have passed the attacking tests) to a CSV string for processing on the database
$attackingUnits = implode(',', $selectedUnits);
// update each attacking unit with the start time of the attack and the unit id we are attacking, as well as any change in movement data
// HERE IS MY PROBLEMATIC QUERY
$sql = "UPDATE Units SET moving = " . $unit['moving'] . ", move_end = " . $unit['move_end'] . ", map_ID = " . $unit['map_ID'] . ", attacking = $attackStartTime, unit_ID_affected = $enemy, updated = now() WHERE unit_ID IN ($attackingUnits);";
$result = mysqli_query($conn, $sql);
// send back the full data array - should only be used for testing and not in production!
echo json_encode($data);
mysqli_close($conn);

Answer 1

OK, after some more web research I found a link that helped me out:
https://stuporglue.org/update-multiple-rows-at-once-with-different-values-in-mysql/
I updated his code to mysqli and after a lot of testing, it works! I can now successfully UPDATE hundreds of rows with one query, rather than sending hundreds of small updates via PHP. Here are the relevant parts of my code for anyone who's interested:
$updateValues = array(); // the array we are going to build out of all the unit values that need to be updated
// build up the query string
$updateValues[$unit["unit_ID"]] = array(
"moving" => $unit["new_start_time"],
"move_end" => $unit["new_end_time"],
"map_ID" => "`destination`",
"destination" => $unit["new_destination"],
"attacking" => 0,
"unit_ID_affected" => 0,
"updated" => "now()"
);
// start of the query
$updateQuery = "UPDATE Units SET ";
// columns we will be updating
$columns = array("moving" => "`moving` = CASE ",
"move_end" => "`move_end` = CASE ",
"map_ID" => "`map_ID` = CASE ",
"destination" => "`destination` = CASE ",
"attacking" => "`attacking` = CASE ",
"unit_ID_affected" => "`unit_ID_affected` = CASE ",
"updated" => "`updated` = CASE ");
// build up each column's CASE statement
foreach ($updateValues as $id => $values) {
$columns['moving'] .= "WHEN `unit_ID` = " . mysqli_real_escape_string($conn, $id) . " THEN " . mysqli_real_escape_string($conn, $values['moving']) . " ";
$columns['move_end'] .= "WHEN `unit_ID` = " . mysqli_real_escape_string($conn, $id) . " THEN " . mysqli_real_escape_string($conn, $values['move_end']) . " ";
$columns['map_ID'] .= "WHEN `unit_ID` = " . mysqli_real_escape_string($conn, $id) . " THEN " . mysqli_real_escape_string($conn, $values['map_ID']) . " ";
$columns['destination'] .= "WHEN `unit_ID` = " . mysqli_real_escape_string($conn, $id) . " THEN " . mysqli_real_escape_string($conn, $values['destination']) . " ";
$columns['attacking'] .= "WHEN `unit_ID` = " . mysqli_real_escape_string($conn, $id) . " THEN " . mysqli_real_escape_string($conn, $values['attacking']) . " ";
$columns['unit_ID_affected'] .= "WHEN `unit_ID` = " . mysqli_real_escape_string($conn, $id) . " THEN " . mysqli_real_escape_string($conn, $values['unit_ID_affected']) . " ";
$columns['updated'] .= "WHEN `unit_ID` = " . mysqli_real_escape_string($conn, $id) . " THEN " . mysqli_real_escape_string($conn, $values['updated']) . " ";
}
// add a default case, here we are going to use whatever value was already in the field
foreach ($columns as $columnName => $queryPart) {
$columns[$columnName] .= " ELSE `$columnName` END ";
}
// build the WHERE part. since we keyed our updateValues off the database keys, this is pretty easy
// $where = " WHERE `unit_ID` = '" . implode("' OR `unit_ID` = '", array_keys($updateValues)) . "'";
$where = " WHERE unit_ID IN ($unitIDs);";
// join the statements with commas, then run the query
$updateQuery .= implode(', ', $columns) . $where;
$result = mysqli_query($conn, $updateQuery);
This will significantly reduce the load on my database as these events can happen every second (think of hundreds of players at once, attacking hundreds of enemy units with hundreds of their own units). I hope this helps someone out.