数据库设计结构

Question

I´m new to database design and never took class on it, i have problem with structuring my database and assigning primary keys.

I have a list of cities, each city has 5 types of public transport. Each type of public transport has different ticket price, main station and CSV file with route coordinations etc. in every city. Then i need to daily calculate average cost of transportation in every city for each type of public transport based on route coordinations (distances), price, time it takes etc.

Table cities :

city (Primary key)

Table public transport :

city, type of transport, ticket price, main station, file1, file2

Table results :

city, type of transport, date, cost

How should i connect these tables (assuming their structure is right)? In table public transport , i think city should be foreign key but type of transport will repeat for every city so i dont think it can be primary key of this table - the same for table results .

Answer 1

The main idea is that you don't wish to repeat ya self. Not only is it an overhead but also it's quite error prone when you wish to change multiple entries that represent the same thing.

There are guidelines on database normalization which help you to ensure that your data is on a form that's easy to maintain and work with.

You don't need to become an expert in understanding which form does what, but being able to identify what should be kept separated is a must when it comes to database designing.

You should list what you know:

• Different cities.
• Different type of transport.
• Different ticket prices.
• Different stations.

If you create a separate table for all of those then it'll be easy to link them together in rows in a table that then represents something on a larger scale. Every entry should have a separate id that will be your primary key, you need to be able to allow eg multiple cities with the same name, thus not being able to hold a unique value if they are to be the primary key.

Eg now it would be easy to identify routes for a city, there can be multiple routes in a city

route_id | city_id | route_name
 1          2         test1
 2          2         test2

You then could add another table that represent which kind of transport is tied with this specific kind of route.

route_id | transport_id
 1          3  
 2          4

You're then able to create a new table that holds points of stations that are a part of your route and you can even identify whether it's a main route or not.

route_connected_id | route_id | station_id | main_route
 1                    1          2            1        // a main route
 2                    1          3            0        // not a main route

And it goes on and on, separating the most simple entries allows you to create complex relationships where all you have to do is link ids.

This is the basic idea which should hopefully get you started, whether you find it helpful or not then I recommend that you take a look on the reading material that I suggested, ie database normalization.