检查数据库中是否存在用户名（PHP）

Question

I think the following code should do the trick, but it still doesn't detect whether the username exists or not.

Here is my code:

//CHECK IF USERNAME ALREADY EXISTS
$query = "SELECT * FROM users WHERE username=" . $_POST['username'];
$result = @mysqli_query($dbc, $query);
if(mysqli_num_rows($result >= 1))
{
    echo '<br><br><span style="color:red;text-align:left;">This userame has already been taken!</span>';
    exit;
}

Anyone know what I'm doing wrong / missing here?

Answer 1

I think you should write it like this:

if(mysqli_num_rows($result) >= 1)

instead of

if(mysqli_num_rows($result >= 1))

mysqli_num_rows returns an int, so in your if statement you have to place a ) after $result

Answer 2

I think you should write it like this:

$query = "SELECT * FROM users WHERE username=" . $_POST['username'];

if ($result = mysqli_query($dbc, $query)) {

     echo '
           <br><br>
           <span style="color:red;text-align:left;">
               This userame has already been taken!
           </span>';
     exit;
}

Answer 3

You missed some quotes and singlequotes.

$query = "SELECT * FROM `users` WHERE `username` = '" . $_POST['username'] ."'";
$result = mysqli_query($dbc, $query) OR DIE(mysqli_error($dbc)); // Dies if there is any error #debugging
$result_rows = mysqli_num_rows($result);
if ($result_rows >= 1) {
    echo '</br></br><span style="color:red;text-align:left;">This userame has already been taken!</span>';
    exit;
}

Using username = '" . $_POST['username'] ."'; instead of " . $_POST['username'];

Then added some debug to the query using OR DIE(mysqli_error($connection)); .

Answer 4

The sql is written incorrectly. The closing double quotes should be outside the closing bracket instead of outside the equal sign. You should have this: $query = "SELECT * FROM users WHERE username= ' ".$_POST['username'] . " ' "; Instead of this:

$query = "SELECT * FROM users WHERE username=" . $_POST['username'];