I'm getting the following error whenever I try to post something with an apostrophe in it:

You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near...

For example when I'm trying to post/using INSERT something like "I'm working hard".It's getting me an error. If I write "I am working hard" everything is fiine.

The code is:

 $sql="INSERT INTO tb_table (`postcontent`, `userid`, `posttime`) VALUES ('".$_POST[content]."', '".$user_id."', '".time()."')";

Any ideas how to fix it?