Looping in php - Creating different roll numbers - php

Question

This is my code:
$roll = rand(100,1000000);
$result = mysql_query("SELECT roll FROM users") or die(mysql_error());
if($row["roll"] == $roll) {
$roll = rand(100,1000000);
}
else
{
mysql_query("INSERT INTO users (roll) VALUES('$roll') ") or die(mysql_error());
}
echo "Data Inserted!";
My question is:
If the regenerated roll number is again equal to a roll number already existing in database, how it should again generate a new roll number and keep on checking it unless it gets a unique number, which i can finally insert in the database? Please help!

Answer 1

You don't have to fetch ALL the rolls each time. It's just a waste of resources. Just check if the roll exists in the database, and if it does, check a new one.
function doesRollExist($roll) {
$sql = "SELECT COUNT(*) FROM users WHERE roll = " . (int)$roll;
$result = mysql_query($sql);
if ($result) {
return ((int)mysql_result($result, 0)) != 0;
}
else {
trigger_error("Query failed: " . mysql_error(), E_USER_ERROR);
}
}
do {
$newRoll = mt_rand(100, 1000000);
}
while (doesRollExist($newRoll));
// Now $newRoll will be a random number that doesn't exist
// in the database.

Answer 2

you can achieve by this way
$flag=1;
while($flag==1)
{
$roll = rand(100,1000000);
$result = mysql_query("SELECT roll FROM users WHERE roll=$roll") or die(mysql_error());
$row = mysql_fetch_row($result);
if($row[0] == $roll)
{
$roll = rand(100,1000000);
}
else
{
$flag=0;
mysql_query("INSERT INTO users values($roll)") or die(mysql_error());
echo "Data Inserted!";
}
}

Answer 3

Try this one:
$count = 1;
while($count > 0) {
$roll = rand(100,1000000);
mysql_query('SELECT COUNT(1) FROM `users` WHERE roll=' . mysql_real_escape($roll)) or die('Can\'t query the DB server.');
$countRow = mysql_fetch_array($result);
$count = $countRow[0];
}
In real-life situations you should probably add better error checking - using trigger_error, or exceptions(that of course have to be caught). I would even recommend to log all the errors.

Answer 4

$roll = rand(100,1000000);
$result = mysql_query("SELECT roll FROM users") or die(mysql_error());
while($row["roll"] == $roll) {
$roll = rand(100,1000000);
}
mysql_query("INSERT INTO users (roll) VALUES('$roll') ") or
die(mysql_error());
echo "Data Inserted!";