Database sessions

When you issue an ALTER SYSTEM KILL SESSION, Oracle merely marks the session as killed and does the actual work of killing the session asynchronously. That may take just a couple seconds, it may take many hours if the session has an uncommitted transaction that did a lot of work that now has to be rolled back or if the session needs to stay around in a killed state in order to notify the client that their session was terminated. It may, therefore, require a substantial amount of waiting before a user could be dropped.

You could do something like this where your loop will wait indefinitely for all the sessions to disappear.

DECLARE
  l_cnt integer;
BEGIN
  EXECUTE IMMEDIATE 'alter user abc_user account lock';
  FOR x IN (SELECT *
              FROM v$session
             WHERE username = 'ABC_USER')
  LOOP
    EXECUTE IMMEDIATE 'alter system kill session ''' || x.sid || ',' || x.serial# || '''';
  END LOOP;

  -- Wait for as long as it takes for all the sessions to go away
  LOOP
    SELECT COUNT(*)
      INTO l_cnt
      FROM v$session
     WHERE username = 'ABC_USER';
    EXIT WHEN l_cnt = 0;
    dbms_lock.sleep( 10 );
  END LOOP;

  EXECUTE IMMEDIATE 'drop user abc_user cascade';
END;

Generally, though, I'd question the problem you're trying to solve. I can't think of many times that it would make sense to drop a user that has active sessions at the time you decide to issue the drop. In the vast majority of cases, the presence of active sessions strongly implies that the account should not be dropped.

Assuming the DATE from user interface can contain times besides 00:00:00 (midnight) and that you only want to know if the DATE from the user interface and the TIMESTAMP fall on the same day (not same hour or minute or ?), try this:

...

myDatabaseDate    DATE;
myDatabaseNextDay DATE;

BEGIN

  -- Change TIMESTAMP to a DATE type with CAST, then TRUNCate time to 00:00:00.
  myDatabaseDate    := TRUNC( CAST(myDatabaseTimeStamp as DATE) );
  myDatabaseNextDay := myDatabaseDate + 1;

  SELECT something into some_var
  FROM MYDATABASE 
  WHERE inputDate < myDatabaseNextDay
  AND inputDate >= myDatabaseDate; 

  ... 

Note 1: Because "inputDate" is a database column and could be indexed, we don't want to do TRUNC(inputDate) because then the index won't be used.

Note 2: Doing the CAST before the SQL statement prevents this PL/SQL compilation warning: PLW-07204: conversion away from column type may result in sub-optimal query plan ... Edit: After testing this on 10.2 XE, even the "myDatabaseDate + 1" causes the warning so, although it seems like doing too much to please the compiler, I added "myDatabaseNextDay := myDatabaseDate + 1;"