Hello,
I am currently facing a design where a table (virtually) needs to store attributes of a topic (related table). The attributes can be user defined, i.e. not known at development type and depend on other factors. Each attributes value can be one of different types (int, int64, double, string) and may have constraints like min, max or length (string). Thus the data type would be modeled as variant in some programming languages, but this is not an option in SQL (beside the MS SQLserver sql_variant extension). So, how to simulate this in SQL. Basically there would be one table describing the attributes type (Type identifier, min/max,.) and one table for the values itself. The design I am currently thinking of would be to make exactly these two tables, with the attributes having a Dataype column and iMin,iMax for integer, i64Min, i64Max, fMin,fMax for double , sMinLen, sMaxLen for strings. The same applies to the value table which will have iValue, i64Value, fValue, string columns to hold the actual data. Now the columns will be filled according to the data type, columns not matching the type will be NULL. This means that each row in the table will have virtual space for any data type which violates database normalization. However it seems to me to be the best deal for performance and data space as NULL takes virtually no room (4/8 bytes in total for a number of fields in some circumstances) and requires no complex queries. One could also imagine to have the constraints moved to a separate table and interpreted according to the data type. Also a table for each type could be imagined but this will make the queries very complicated working against performance. Note: The model has to work for huge databases Anybody has a better alternative ?
