Mysql insert with foreign key referring to primary id

Question

Let's say I hava a table

object:

id, primary key auto-increment
obj_id, foreign key (object.id)
val, integer

Is it possible to insert a record with obj_id = id. Not having an error with foreign key constraint?

Insert into object (val) values (123)

Answer 1

Yes, that's totally ok.

Answer 2

If obj_id allows null then it is ok.

EDIT:

What are you trying to achieve? You said it is a foreign key then it should be the value from that table. If you want another column having same data as your PK value then this column should not be the foreign key and you need to write trigger to update that column or some other approach.