Hur man kontrollerar om värde finns i en MySQL-databas

föredraget sätt, med MySQLi-tillägget:

$mysqli = new mysqli(SERVER, DBUSER, DBPASS, DATABASE);
$result = $mysqli->query("SELECT id FROM mytable WHERE city = 'c7'");
if($result->num_rows == 0) {
     // row not found, do stuff...
} else {
    // do other stuff...
}
$mysqli->close();

utfasad:

$result = mysql_query("SELECT id FROM mytable WHERE city = 'c7'");
if(mysql_num_rows($result) == 0) {
     // row not found, do stuff...
} else {
    // do other stuff...
}