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mysqlsqldatabasedatabase-abstraction

MySQL: Fields length. Does it really matter?

I'm working with some database abstraction layers and most of them are using attributes like "String" which is VARCHAR 250 or INTEGER which has length of 11 digits. But for example I have something that will be less than 250 characters long. Should I go and make it less? Does it really makes any valuable difference?

Thanks in advance!

Solution

  • INT length does nothing. All INTs are 4 bytes. The number you can set, is only used for zerofill (and who uses that!?).

    VARCHAR length does more. It's the maxlength of the field. VARCHAR is saved so that only the actual data is stored, so the length doesn't mattter. These days, you can have bigger VARCHARs than 255 bytes (being 256^2-1). The difference is the bytes that are used for the field length. VARCHAR(100) and VARCHAR(8) and VARCHAR(255) use 1 byte to save the field length. VARCHAR(1000) uses 2.

    Hope that helps =)

    edit
    I almost always make my VARCHARs 250 long. Actual length should be checked in the app anyway. For bigger fields I use TEXT (and those are stored differently, so can be much much longer).

    edit
    I don't know how current this is, but it used to help me (understand): http://help.scibit.com/Mascon/masconMySQL_Field_Types.html