与MySQL插入命令相反[关闭]

What is the opposite of the MySQL INSERT Command?

I want to know how to delete users from a table without admin. I Googled everywhere but couldn't find it at all.

Here is my PHP file:

<?php
$username = $_POST["username"];
$password = $_POST["password"];
$passcheck = $_POST["passcheck"];
$email = $_POST["email"];
if ( $username && $password && $passcheck && $email ) {
} else
    echo "Please enter all fields";
?>
...
<form action="register.php" method="post">
    <input type="text" name="username"><br>
    <input type="password" name="password"><br>
    <input type="password" name="passcheck"><br>
    <input type="text" name="email"><br>
    <input type="submit" value="Register">
</form>
<?php
$username = $_POST["username"];
$password = $_POST["password"];
$passcheck = $_POST["passcheck"];
$email = $_POST["email"];
if ( $username && $password && $passcheck && $email ) {
    $connect = mysql_connect( "localhost", "root", "root" ) or die("Couldn't connect!");
    mysql_select_db("login") or die("Couldn't find database!");
    $query = mysql_query( "SELECT * FROM users WHERE username='$username'" );
    $numrows = mysql_num_rows( $query );
        if ( $numrows != 0 ) {
        echo "Username taken";
    } else
        if ( $password == $passcheck ) {
            mysql_query("INSERT INTO users (username, password, email)
                VALUES ('$username','$password','$email')");
        } else
            echo "Passwords don't match";
} else
    echo "Please enter all fields";
?>

The MySQL Delete statement is:

DELETE FROM table_name WHERE some_column = some_value;

Take a look here: http://www.w3schools.com/php/php_mysql_delete.asp

DELETE FROM some_table WHERE some_value=X;