MYSQLi PHP connect - mysqli

Question

Is the following a valid mysqli php connect insert statement?
if($mysql_query = $conn->query("INSERT INTO users (username,password,question,securityanswer) VALUES ('$uname','$upass','$selectquestion','$answer')"))
{
?>
<script>alert('successfully registered ');</script>
<?php
}
else
{
?>
<script>alert('error while registering you...');</script>
<?php
}
}
However I am getting error as "error while registering you..."
Thanks

Answer 1

Issue is resolved. There was an issue with the "user_id" column primary key which was being updated duplicate(0 value) with this error "Duplicate entry '0' for key 'PRIMARY'. Upon updating user_id column with auto increment in phpmyadmin, the INSERT query got updated successfully.
Using the below code to check for errors helped.
die(mysqli_error($conn));

Answer 2

A simple example:
<?php
//Create the connection
$con = mysqli_connect("HostName","UserName","password","DBName") or die("Some error occurred during connection " . mysqli_error($con));
// Write query
$strSQL = "SELECT username FROM MyTable";
// Execute the query.
$query = mysqli_query($con, $strSQL);
while($result = mysqli_fetch_array($query))
{
echo $result["username"]."
";
}
// Close the connection
mysqli_close($con);
?>

Answer 3

Can you paste the whole block with connection statement?
Otherwise SQL statement looks fine. Excepct you should escape inputs to MySQL
if($mysql_query = $conn->query("INSERT INTO users (username,password,question,securityanswer) VALUES ('$uname','$upass','$selectquestion','$answer')"))
Why using if($mysql_query = $conn->query ?
better
if($conn->query("INSERT INTO users (username,password,question,securityanswer) VALUES ('$uname','$upass','$selectquestion','$answer')") === TRUE)