How to delete rows in tables that contain foreign keys to other tables

Question

Suppose there is a main table containing a primary key and there is another table which contains a foreign key to this main table. So if we delete the row of main table it w

Answer 1

From your question, I think it is safe to assume you have CASCADING DELETES turned on.
All that is needed in that case is

DELETE FROM MainTable
WHERE PrimaryKey = ???

You database engine will take care of deleting the corresponding referencing records.