How so. In most schema-free db's the missing alter table feature is not needed. maybe you meant the quotes to be in a different place? missing "alter table problem" perhaps?
You won't get O(1) since scheme-free dbs are not organized around columns/fields in the same way a traditional db is all about rows and columns, but just about every one I am aware of let's you create an index on a particular field so at least you get O(n). Given the infrequent use of this operation I am happy to leave it in the "O(n) is good enough" category in return for the other benefits an efficiencies that a schema-free db offer.
Well, you can get both with Hypertable, where you can alter table to add/drop column families in O(1) time, while still have schema free benefits with column qualifiers.
