Mysql concat查询不起作用

This query did not update the table in Mysql database:

mysql_query("UPDATE users 
SET friend_array=CONCAT(users.friend_array,'$user_to') 
WHERE username='$user_from'");

Hi From given info I can say only that add this die(mysql_error()); after execution of query this will give you your error. Also add these two lines at the top of your php file

error_reporting(E_ALL);
ini_set('display_errors',1);

mysql_query("UPDATE users 
SET friend_array=CONCAT(users.friend_array,'$user_to') 
WHERE username='$user_from'") or die(mysql_error());

And Please don't use mysqlit is deprecated now instead use mysqli or other