Script to update 5500 fields in a telephone type column with random numbers - mysqli

Question

I would need to create a php7 script that generates 5500 random telephone numbers starting with the example number 3
"3471239900". The script should go to overwrite the data already present.
/**
* genera numero tel casuale che inizia per 3
*/
function telefono()
{
$telefono = '';
for ($k=0; $k<9; $k++) {
//genera casuale 9 cifre
$telefono .= rand(0, 9);
}
//inizia per 3
return '3' . $telefono;
}
$res = mysqli_query($conn, 'SELECT id_com FROM commesse ORDER BY id_com');
while ($riga = mysqli_fetch_assoc($res)) {
$id = (int)$riga['id_com'];
$query = "UPDATE commesse SET cliente=tel='".telefono()."' WHERE id_com=" . $id_com;
}

Answer 1

You don't need to invent such code to fill a single column in a database table with random numbers.
Following update statement will populate cliente_tel column of the commesse table with 10 digit random numbers all beginning with 3.
UPDATE
`commesse`
SET
`cliente_tel` = CONCAT("3",ROUND(RAND()*(999999999-100000000)[phone]))
WHERE 1;
Using ROUND() is necessary here since RAND() returns a float between 0 and 1.
Good to remember: Running any kind of update/insert statement in a loop is always expensive and slow. Try to avoid running SQL queries in a loop as much as possible.