How to make such a MySQL fetch?

Question

MySQL

Here is a table with routes and a selection by line, so in order not to confuse, I will simplify the background and take fictitious tables.
Table A
(id ,name)
Table B
(id, A_id, str_here)
You need to select all those A , Where B.str_here are equal to the same str_here of that record A, according to which we take the rest of the records or such str_here for those A records are null, that is, simply no .

Answer 1

and now we translate our question into English and see what happened;)