How to display a url in php which end part is stored in mysql

How to display a url in php which end part is stored in mysql

I'm trying to create a form in which a user inserts their youtube code
into a field, which is then stored in mysql.
When the code is added to the end of this link -
//www.youtube.com/embed/[code here] - it displays the video.
How can I do it so that the link is permanently fixed in the php document
and the end part is retrieved from mysql in a way that when the page is
opened it displays the video correctly?
Very simple stuff when you know how to do it but I don't so I would
appreciate if someone could tell me the way of doing this.
thanks! Eugenie