Databases, Assignment 1
                        16 August, 2010
                      Due 30 August, 2010

You will be provided with a MySQL database containing information
about trains on Indian Railways.  (Instructions on how to obtain
and load the database are given separately).

This database has three tables, "schedule", "stations" and
"terminus" that are described in more detail below.

You have to write (a sequence of) SQL queries to construct a
table listing all pairs of stations (A,B) where A and B are from
the list of terminus stations specified in the table "terminus"
such that one can go from A to B with at most two changes of
train.

Your output should be a table of the form:

(StationA, StationB, Train1, Change1, Train2, Change2, Train3)

If there is a direct train, the columns from Change1 onwards will
be empty.

If one change is required, Train1 is the train originating from
StationA, Change1 is the station where one changes trains and
Train2 is the second train that reaches Station B.  Change2 and
Train3 will be empty.

If two changes are required, Train1 is the train originating from
StationA, Change1 is the station where one changes from Train1 to
Train2, Change2 is the station where one changes from Train2 to
Train3 and Train3 reaches StationB.

In this table, StationA, StationB, Change1 and Change2 should all
be in terms of the abbreviated station codes while Train1, Train2
and Train3 will be in terms of the train numbers.

Needless to say, in any row of the table, no two stations and
no two trains should be the same.

======================================================================
List of tables and description
======================================================================
schedule
+---------+------------+
| Field   | Type       |
+---------+------------+
| train   | int(11)    | 
| station | varchar(6) | 
| arr     | time       | 
| arrdate | int(11)    | 
| dep     | time       | 
| depdate | int(11)    |
+---------+------------+

This table describes each train, one stop at a time.  A row in
the table of the form

  (N, S, T1, D1, T2, D2)

indicates that train N arrives at station S1 at time T1 on day D1
and leaves at time T2 on day D2.

For the originating station of a train, T1 and D1 will be blank,
while for the final station, T2 and D2 will be blank.

Trains are identified by their number, stations by their station
code.  Since a train journey may last over multiple days, the
arrival and departure times are accompanied by the "day number".
Each train starts on day 0, so all stops on the first day have
day number 0, stops on the second day have day number 1 etc.  

For instance, if train 8888 originates from Chennai Central (MAS)
at 2345 and next stops at Arakkonam (AJJ) at 0045 for 10 minutes,
the corresponding entries in the table "schedule" will be

   (8888,MAS,NULL,NULL,2345,0)
   (8888,AJJ,0045,1,0055,1)

----------------------------------------------------------------------

stations
+---------+-------------+
| Field   | Type        |
+---------+-------------+
| station | varchar(5)  | 
| name    | varchar(20) | 
+---------+-------------+

Lists out the station name for each station code.

----------------------------------------------------------------------

terminus
+---------+-------------+
| Field   | Type        |
+---------+-------------+
| station | varchar(5)  | 
| name    | varchar(20) | 
+---------+-------------+

Subset of stations from the table "station".
======================================================================