如果数据库行= null，则打印一些内容，否则打印其他内容

I'm trying to do a seat booking system, and i need to check via MySQL if the seat X is available. If there is a name assigned to it, print "sorry, this seat is already taken", else if there is no name assigned to it (default 0), print "available!".

This is what i tried:

<?php
$link = mysql_connect(localhost, root, root);
mysql_select_db(room); 
if (!$link) {
    die('Could not connect: ' . mysql_error());
}

$result  = mysql_query("SELECT name FROM seats WHERE seat = 'A1'");
if ($result  == '0') {
        echo 'available!';
    } else {
        echo 'Sorry, this seat is already taken.';
    }
}
?>

You should considered moving away from the mysql_* functions. Either way, you should be doing something like this:

http://php.net/manual/en/function.mysql-num-rows.php

$result  = mysql_query("SELECT name FROM seats WHERE seat = 'A1'");
if (mysql_num_rows($results) == 0) {
    echo 'available!';
} else {
    echo 'Sorry, this seat is already taken.';
}

You've also got an extra } at the end.

Try this :

$result  = mysql_query("SELECT name FROM seats WHERE seat = 'A1'");
     if (mysql_num_rows($result)==0) {
        echo 'available!';
     }else {
            echo 'Sorry, this seat is already taken.';
        }

Try this:

<?php
$link = new mysqli("localhost", "root", "root", "room");
if ($link->connect_errno)
{
    die('Could not connect: ' . $mysqli->connect_error);
}

if (($result = $link->query("SELECT name FROM seats WHERE seat = 'A1'") && $result->num_rows)
{
    echo 'Sorry, this seat is already taken.';
}
else
{
    $result->close();
    echo 'available!';
}

This is using the new MySQLi library and should properly check whether a result was returned with any rows. Checking $result->num_rows may not be necessary, as $result should be empty if no rows were returned.