Re: Cost of joins?

[Alec.Cawley]

"Martijn Tonies" <m.tonies@stripped> wrote on 09/07/2004 13:55:40:

> If you're de-normalizing
> your design to get better performance, then there's something
> wrong with the database engine (whatever engine that may be).

Nearly always, but not absolutely always. I have a table with columns 
        primary start
        primary finish
        secondary start
        secondary finish

Since it is defined that the distance between start and finish is the same 
for both primary and secondary, this is denormalised, since secondary 
finish is always given by secondary start + (primary finish - primary 
start). However, I want to use all four fields as indexes, including 
secondary finish. Does any database allow indexes on complex functions of 
columns rather than on columns themselves? Or is this just a defect in 
MySQL?

        Alec