Integer vs String in database

in my opinion for postal codes you have to use strings, because you can have postal codes that stards with zeros (09100) and if you use integers it would be 9100: sorting is not a problem, because there is still an alphabetical order ('09100' comes before '09101'). For Storing file numbers I would expect an interger, so you don't have any problem in incresing / decreasing its number. So integer vs strings depends upon the use you make!

In my country, post-codes are also always 4 digits. But the first digit can be zero.

If you store "0700" as an integer, you can get a lot of problems:

• It may be read as an octal value
• If it is read correctly as a decimal value, it gets turned into "700"
• When you get the value "700", you must remember to add the zero
• I you don't add the zero, later on, how will you know if "700" is "0700", or someone mistyped "7100"?

Technically, our post codes is actually strings, even if it is always 4 digits.

You can store them as integers, to save space. But remember this is a simple DB-trick, and be careful about leading zeroes.

But what about for storing how many files are in a torrent? Integer or string?

That's clearly an integer.

I always use the following rule:

If you plan on performing mathematical calculations on it (adding/subtracting/etc) make it an integer or other numerical data type.

If you do not plan on performing any types of mathematical calculations on the field, store it as a string.

In the instance of Zip codes, you should never have a time where you need to add to a zip code, or subtract, or multiply two zip codes together. Mathematical functions generally are not used on ZIP codes because they are used as identifiers and not quantities. Therefore you should store your zip code as a string datatype