Yes.In the CHECK condition for a column of a table, we can reference some other column of the same table and thus enforce self referential integrity.

The & operator means that the PL SQL block requires user input for a variable. The && operator means that the value of this variable should be the same as inputted by the user previously for this same variable.

Explicit cursors can take parameters, as the example below shows.A cursor parameter can appear in a query wherever a constant can appear.
CURSOR c1 (median IN NUMBER) IS
SELECT job, ename FROM emp WHERE sal > median;

The types of Rollback sagments are as follows :

1. Public Available to all instances
2. Private Available to specific instance.

In a Single Threaded Architecture (or a dedicated server configuration) the database manager creates a separate process for each database user.But in MTA the database manager can assign multiple users (multiple user processes) to a single dispatcher (server process), a controlling process that queues request for work thus reducing the databases memory requirement and resources.