Get and update column of all rows in a table - php

Question

I'm developing a game and I want a script to run every minute (with the help of cron job, I guess).
So the script that I want to run takes the maximum HP of a character (from a column in a database table), calculates to get 10% of that value and then add those 10% to the characters current hp (which is another column in the table). I then want to iterate this over all rows in the database table.
E.g. consider the following table:
charname current_hp max_hp
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
player1 20 30
player2 15 64
player3 38 38
After the script has been run, I want the table to look like this:
charname current_hp max_hp
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
player1 23 30
player2 21 64
player3 38 38
So, I know how I technically could implement this, e.g.
$characters = $db->getCharacterList();
foreach ($characters as $character) {
$maxHp = $character['max_hp'];
$curHp = $character['current_hp'];
$hpToAdd = $maxHp / 10;
if (($curHp + $hpToAdd) >= $maxHp) {
$db->update('characters', $character['id'], array(
'current_hp' => $maxHp
));
} else {
$db->update('characters', $character['id'], array(
'current_hp' => ($curHp + $hpToAdd)
));
}
}
My only question is: Is the solution posted above an efficient way to implement this? Will this work on a table with, say, 10 000 rows, or will it take too long?
Thanks in advance.

Answer 1

Are you using a SQL database? If you have 10,000 rows, your solution will hit the database 10,000 times. A SQL statement like this will only make one database hit:
UPDATE characters
SET current_hp = LEAST(max_hp, current_hp + (max_hp / 10))
The database will still have to do the I/O necessary to update all 10,000 rows, but it will happen more efficiently than thousands of individual queries.

Answer 2

In One SQL statement will do all your requirements for more performance remove any indexes on this table to keep it fast
UPDATE test
SET current_hp= CASE
WHEN ((max_hp/10)+current_hp) >=max_hp THEN max_hp
ELSE ((max_hp/10)+current_hp)
END