There is no problem with the code, why is it failing? "The ID inserted by the current user is 0"

Question

<?php

if (trim($_POST['password']) != trim($_POST['repassword'])) {

exit('twice The password is inconsistent, please return to the previous page');

}

$username = trim($_POST['username']);

$password = md5(trim ($_POST['password']));

$time = time();

$ip = $_SERVER['REMOTE_ADDR'];

$conn = mysqli_connect('localhost', 'root', 'root');

//If there is an error, there is an error number
if (mysqli_errno($conn)) {

echo mysqli_error ($conn);

exit;
}

mysqli_select_db($conn, 'text');

mysqli_set_charset($conn, 'utf8');

$sql = "insert into user(username,password,createtime,createip) values('" . $username . "','" . $password . "','" . $time . "', '" . $ip . "')";

$result = mysqli_query($conn, $sql);

if ($result) {
echo 'success';
} else {
echo 'failed';

}

echo 'The ID inserted by the current user is' . mysqli_insert_id($conn);

mysqli_close( $conn);

?>

Answer 1

Check if there is already that record in the database, it cannot be repeated

Answer 2

1. Whether the sql statement corresponds to the database field

2. Field issues in the sql statement
   

$ sql = "insert into user(`username`,`password`,`createtime`,`createip`) values ​​('" . $username . "','" . $password . "','" . $time . " ','" . $ip . "')";