PHP If Else statement not working for database - php

Question

Ok, I'm confused. I have some code that searches a database table for a username, and then uses an if else statement to run some code depending on if the user is found or not. My code is below. The problem is that the code isn't even seeing the if else statement, and I have no idea why. Any help is appreciated.
$sqluser = "select * from users where username='" . $user ."'"; //Searching to see if the user is in the database
echo $sqluser . "<br><br>"; //writes out the select statement to make sure it is correct
$query = mssql_query($sqluser); //returns the results
$num_rows = mssql_num_rows($query); //gets the number of rows returned
echo $num_rows; //writes out the number of rows
if ($num_rows==0) //determines what happens next if the user exists or not
{
//displays an error box if the user doesn't exist
echo "<script type=text/javascript>";
echo "alert('That user doesn't exist. Please try again.')";
echo "</script>";
}
else
{
//will be code to run if the user does exist
echo "<script type=text/javascript>alert('Testing.')</script>";
}

Answer 1

I couldn't add a comment. So I will write this as an answer instead.
Since you state that the alert JavaScript is showing in the page source, this mean that the IF/ELSE statement in PHP is working fine. The problem is with the single quote. You have a single quote inside a single quoted alert function. Hence the JavaScript alert function cannot be executed.
echo "alert('That user doesn't exist. Please try again.')";
Try using this instead
echo "alert('That user doesn\'t exist. Please try again.');";