PHP+MYSQL不能写入数据，求高手看看！下面是代码

$mysql_username="root";
$mysql_userpass="123456";
$mysql_server="localhost";
$mysql_database="web";

$conn=mysql_connect($mysql_server,$mysql_username,$mysql_userpass) or die("不能连接数据库服务器！");
mysql_select_db($mysql_database,$conn);
mysql_query ('set names "gbk"');

$sql="INSERT INTO `news` ( `id` , `classid` , `title` , `content` , `addtime` , `hits` , `yn` , `tj` , `editor` , `from` , `writer` , `keywd` , `fcolor` , `photo` , `introduce` )VALUES (NULL , '$classid', '$title', '$content', 'date()', '$hits', '$yn', '$tj', '$editor', '$from', '$writer', '$keywd', '$fcolor', '$photo', '$introduce')";

mysql_query($sql);