Calling a function for each MySQL row - php

Question

I have a standard MySQL database, with around 60 rows (as in user accounts). When I first made it I made the mistake of making session IDs the same as the simple account ID, now I want to fix my mistake and I am obviously not going to go through 60 rows to reset them different secure session IDs, so I am writing this function:
function generate_sessionid(){
return bin2hex(openssl_random_pseudo_bytes(32));
}
function assign_all_sessionids(){
$sessionid = generate_sessionid();
$conn = sql_connect();
$result = mysqli_query($conn, "UPDATE accounts SET sessionid='$sessionid' WHERE 1");
sql_disconnect($conn);
}
assign_all_sessionids();
Problem: Every account in the database gets the same random session ID as the rest. How do I make it recall the function for each row in order to allow it to be random for each row?

Answer 1

Try get user's count from DB and simply execute it N times
function assign_all_sessionids(){
$conn = sql_connect();
// getting users count
// here just change 'id' to your id parameter
$result = mysqli_query($conn, "SELECT id FROM accounts");
$arr = $result->fetch_array(MYSQLI_NUM);
// executing N times
for($i = 0; $i < $result->num_rows; $i++){
$sessionid = generate_sessionid();
// here just change 'id' to your id parameter again
mysqli_query($conn, "UPDATE accounts SET sessionid='$sessionid' WHERE `id`=".$arr[$i]);
}
sql_disconnect($conn);
}

Answer 2

You can do what you want by first setting all the session ids to NULL:
UPDATE accounts
SET sessionid = NULL;
Then, inside the loop:
UPDATE accounts
SET sessionid = '$sessionid'
WHERE sessionid IS NOT NULL
LIMIT 1;

Answer 3

Normally you don't want to execute queries in a loop, however in this case you need to get all of the current unique identifiers, loop and generate a new identifier and then update one:
function assign_all_sessionids(){
$conn = mysqli_connect('whatever...');
$select = mysqli_query($conn, "SELECT sessionid FROM accounts");
while(list($id) = mysqli_fetch_assoc($select)) {
$sessionid = generate_sessionid();
$update = mysqli_query($conn, "UPDATE accounts SET sessionid='$sessionid' WHERE sessionid='$id'");
}
}