How to check user already present in database change the username - php

Question

// php code start------------->
<?php
// define variables and set to empty values
$nameErr=$empidErr=$usernameErr=$passwordErr="";
$name=$empid=$username=$password="";
if(isset($_POST['submit']))
{
if (empty($_POST["empid"])) {
$empid = "";
} else {
$empid = test_input($_POST["empid"]);
}
if (empty($_POST["name"])) {
$name = "";
} else {
$name = test_input($_POST["name"]);
}
if (empty($_POST["etype"])) {
$etype = "";
} else {
$etype = test_input($_POST["etype"]);
}
if (empty($_POST["username"])) {
$usernameErr = "Username is required";
} else {
$username = test_input($_POST["username"]);
// check if name only contains letters and whitespace
if (!preg_match("/[0-9A-Za-z ^-_#. ]*$/",$username)) {
$usernameErr = "Only letters and white space allowed";
}
}
if (empty($_POST["password"])) {
$passwordErr = "Password is required";
} else {
$password = test_input($_POST["password"]);
// check if name only contains letters and whitespace
if (!preg_match("/[0-9A-Za-z ^-_#. ]*$/",$password)) {
$passwordErr = "Only letters and white space allowed";
}
}
}
//collect the data
function test_input($data) {
$data = trim($data);
$data = stripslashes($data);
$data = htmlspecialchars($data);
return $data;
}
if((strlen($name)>0)&&(strlen($empid)>0)&&(strlen($etype)>0)&&(strlen($username)>0)&&(strlen($password)>0))
{
include "connection.php";
//Here to check the username is aleady present in database or not
$query = mysql_query("SELECT * FROM signin WHERE username='$username' ", $con);
//$result = mysql_query($query) or die('Error: ' . mysqli_error($con));
if (mysql_num_rows($query) <=0)
{
echo "<script>alert('User already Exists Change the username');</script>";
echo"<script>window.location.href = 'signin.php';</script>";
}
else
{
//if not present in database then create the new user in database.
$sql="INSERT INTO signin (emp_name,emp_id,emp_type,username,password,create_datetime)
VALUES ('$name','$empid','$etype','$username','$password',now())";
if (!mysqli_query($con,$sql)) {
die('Error: ' . mysqli_error($con));
}
echo "<script>alert('New User Added Successfully');</script>";
echo"<script>window.location.href = 'login.php';</script>";
}
mysqli_close($con);
}
?>
//php code end------------<
//html code------------------>
<form method="post" action="<?php echo htmlspecialchars($_SERVER["PHP_SELF"]);?>">
<fieldset>
<legend> <b><i> Information</i></b></legend><br>
Employee ID:-<input type="text" name="empid" placeholder="Enter Employee ID" size="10" value="<?php echo $rum1?>" readonly>
Employee Name:-<input type="text" name="name" placeholder="Surname Middlename Father Name" size="50" value="<?php echo $rum2;?>" readonly>
Employee Type:-<input type="text" name="etype" placeholder="Type" value="<?php echo $rum3;?>" readonly><br /><br />
Username:-<input type="text" name="username" id="loginid" placeholder="Username" size="30" value="<?php echo $unm;?>">
<span class="error">* <?php echo $usernameErr;?></span> <br /><br />
Password:-<input type="password" id="password" name="password" size="30">
<span class="error">* <?php echo $passwordErr;?></span> <br />
</fieldset>
<br>
<input name="submit" type="submit" value="Submit">
<input name="reset" type="submit" value="Reset">
<br ><br >
</form>
</fieldset>
</body>
</html>
//html code end---------------------<
In above php code is work but i want to check username.if the username present in the database then give the alert as the user is already present in the database change the username please. So please sir or madam suggest any code or changes in this php code and suggest any solution to check the user present in database or not.if user first time register then new user is added and if user multiple second time register then give alert is user already register please do your login.

Answer 1

to know if present mysql_num_rows should return 1 or special cases more than one
so change this
if (mysql_num_rows($query) <=0)
{
echo "<script>alert('User already Exists Change the username');</script>";
echo"<script>window.location.href = 'signin.php';</script>";
}
To this
if (mysql_num_rows($query) >0)
{
echo "<script>alert('User already Exists Change the username');</script>";
echo"<script>window.location.href = 'signin.php';</script>";
}
Dont use mysql function as they are depriciated. Learn mysqli or PDO