I need to create a database containing all cities and zip codes worldwide. For that I want to create a table 'city' and a table zip_code. My question is, how is the relation between city and zip code, is it worldwide an 1:n relationship or can it also be m:n in some countries?
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It differs. In Holland we got multiple zipcodes per street, most of the time. The zip codes are so fine grained (consisting of 4 digits + 2 letters), that just the zipcode and the address house number is enough to uniquely identify a building.
In Belgium, though, there's a 4 digit postal code, and a couple of towns can have the same zipcode, while it is still possible that a larger city has multiple zipcodes. It can even happen that a city has multiple zipcodes, while each (or some) of them are shared with some smaller towns as well.
So I would almost say that there is not relation between zip code and city, or at least no one definition that works on a global scale. If you would store it in a database, then it's definately a m:n relation.
于 2013-08-14T18:44:26.627 回答
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For the US at least it is a M:M. A city can have multiplle zips, and a zip can cover more than one city, (Obviously depending on how loosly you define a city vs a town or a municipality).
于 2013-08-14T18:45:18.090 回答