Mysql – Critique the MySQL Database Design for Unlimited DYNAMIC Fields


Looking for a scalable, flexible and fast database design for 'Build your own form' style website – e.g Wufoo.


  1. User has only 1 Form they can build
  2. User can create their own fields or choose from 'standard' fields
  3. User's 1 Form has as many fields as the user wants
  4. Values can be the sibling of another value E.g A photo value could have name, location, width, height as sibling values

Special Rules:

  1. User can submit their form a maximum of 5 times a day
  2. Value's Date is important
  3. Flexibility to report on values (for single user, across all users, 1 field, many fields) is very important — data visualization (most will be chronologically based e.g. all photos for July 2009 for all users).

Table "users"


Table "field_user" – assign a field to a users form



weight – int – used to order the fields on the users form

Table "fields"


creator_uid – int – the field 'creator'

label – varchar – e.g. Email

value_type – varchar – used to determine what field in the 'values' table will be filled in (e.g. if 'int' then values of this field will submit data into the values.type_int field – and all other .type_x fields will be NULL).

field_type – varchar – e.g. 'email' – used for special conditions e.g. validation rules

Table "values"





date – date

date_group – int – value 1-5 (user may submit max of 5 forms per day)

type_varchar – varchar

type_text – text

type_int – int

type_float – float

type_bool – bool

type_date – date

type_timestamp – timestamp

I understand that this approach will mean records in the 'Value' table will only have 1 piece of data with other .type_x fields containing NULL's… but from my understanding this design will be the 'fastest' solution (less queries, less join tables)

Best Solution

At OSCON yesterday, Josh Berkus gave a good tutorial on DB design, and he spent a good fraction of it mercilessly tearing into such "EAV"il tables; you should be able to find his slides on the OSCON site soon, and eventually the audio recording of his whole tutorial online (the latter will probably take a while).

You'll need a join per attribute (multiple instances of the values table, one per attribute you're fetching or updating) so I don't know what you mean by "less join tables". Joining many instances of the same table isn't a particularly fast operation, and your design makes indices nearly unfeasible and unusable.

At least as a minor improvement use per-type separate tables for your attributes' values (maybe some indexing might be applicable in that case, though with MySQL's limitation to one index per query per table even that's somewhat dubious).