Storing data in a 2d matrix

Question

i have to store data of the bus routes between two bus stops
i need to save it as a matrix
how to design a table or tables for it?
stop1 stop2 stop3
stop1 -1 a b
stop2 a -1 c
stop3 b c -1

Answer 1

shashank2 wrote:
i have to store data of the bus routes between two bus stops
i need to save it as a matrix
how to design a table or tables for it?
stop1 stop2 stop3
stop1 -1 a b
stop2 a -1 c
stop3 b c -1Hi,
As Sentinel said, don't confuse how data appears with how data is stored.
The same data can appear in lots of different ways in different reports.
In a relational database, each kind of object, or entity, is usually stored in a separate table.
For example, it seems your data concerns two entities, bus routes and stops. So you should probably have a route table and a stop table.
The route table will contain attributes of the route (that is, things that define or describe the route, such as route number, date opened, total length, ...). Each route will have at (most one) of each attribute. (that is, there wlll only be one route_number column).
The stop table will contain attributes of the stops (stop name, coordinates, description of facilities, ...) Each stop will have (at most) one of each.
Now, how should we record the fact that route a stops at stop1?
'stop1' is not an attribute of the route, since route a also stops at stop2.
'a' is not an attribute of the stop, since route b also stops at stop1.
There is a many-to-many relationship between routes and stops: each route (presumably) goes to many stops, and each stop (might possibly) serve many routes.
Typically, a many-to-many relationship between two entities is stored in a separate table, with pointers (columns with the same value as some column in another table) to the separate entity tables.
For example:
CREATE TABLE     route_stop
(     route_id     VARCHAR2 (10)
,     stop_id          VARCHAR2 (10)
INSERT INTO route_stop (route_id, stop_id) VALUES ('a', 'stop1');
INSERT INTO route_stop (route_id, stop_id) VALUES ('a', 'stop2');
INSERT INTO route_stop (route_id, stop_id) VALUES ('b', 'stop1');
INSERT INTO route_stop (route_id, stop_id) VALUES ('b', 'stop3');
INSERT INTO route_stop (route_id, stop_id) VALUES ('c', 'stop2');
INSERT INTO route_stop (route_id, stop_id) VALUES ('c', 'stop3');I haven't shown the route, which contains a column with the values 'a', 'b', and 'c',
or the stop table, that contains the values 'stop1', stop2', 'stop3'.
In a good relational design, data is stored in one place only.
The fact that route a goes to stop1 only has to be recorded in one place, the route_stop table.
If the route changes in the future, and route a no longer goes to stop1, you will only have to change one row of one table.
As Sentinel said, you can display this data as a matrix if you need to:
WITH     all_pairs     AS
     SELECT     a.route_id
     ,     a.stop_id     AS from_id
     ,     b.stop_id     AS to_id
     FROM     route_stop     a
     JOIN     route_stop     b  ON     a.route_id =  b.route_id
                       AND     a.stop_id  != b.stop_id
SELECT     from_id
,     NVL     ( MAX (CASE WHEN to_id = 'stop1' THEN route_id END)
          , '-1'
          )               AS stop1
,     NVL     ( MAX (CASE WHEN to_id = 'stop2' THEN route_id END)
          , '-1'
          )               AS stop2
,     NVL     ( MAX (CASE WHEN to_id = 'stop3' THEN route_id END)
          , '-1'
          )               AS stop3
FROM     all_pairs
GROUP BY     from_id
ORDER BY     from_id;The query above produces the results below:
FROM_ID    STOP1      STOP2      STOP3
stop1      -1         a          b
stop2      a          -1         c
stop3      b          c          -1The sub-query all_pairs above is a lot like Sentinel's my_2d_routes table.
For purposes of this query, it's convenient to have rendundant data (for example, one row that says
route 'a' goes to 'stop1' and 'stop2', and another row that says
route 'a' goes to 'stop2' and 'stop1', but this does not need to be stored permanently in any table.
Note that '-1' is not stored in any table.
It is not an attribute of any route, stop, or route_stop. It's merely part of the display you want for this query.