UPDATE concat and variables

问题

I might just be sleepy, but i've tried to concat this in various ways and it just isn't working. the $friend_id is simply a string, and shouldn't be causing a problem as far as I know.

mysql_query("UPDATE users SET friends =  CONCAT(friends,"$friend_id")  WHERE username = '$user_logged_in'") or die mysql_error());

or

mysql_query("UPDATE users SET friends = friends +" . ", " . "'$friend_id' WHERE username = '$user_logged_in'");

any ideas where im tripping up?

回答1:

This is what worked in the end.

mysql_query("UPDATE users SET friends = CONCAT(friends,'".",".$friend_id."') WHERE username = '$user_logged_in'");

回答2:

try this

mysql_query("UPDATE users SET friends =  CONCAT(friends,'".$friend_id."')  WHERE username = '".$user_logged_in."'") or die mysql_error());

回答3:

Use . to concat string in PHP.

mysql_query("UPDATE users SET friends =  CONCAT(friends,".$friend_id.")  WHERE username = '$user_logged_in'") or die mysql_error());

回答4:

Before run the query please check your variable "$friend_id". I just trimmed ",".

$friend_id = trim($friend_id, ',');

Query:

mysql_query("UPDATE users SET friends =  CONCAT(friends,'".$friend_id."')  WHERE username = '".$user_logged_in."'") or die mysql_error());

来源：https://stackoverflow.com/questions/13098371/update-concat-and-variables