what is the risk of using sparse columns instead of normal relational tables?

Question

I have three table that related to one table,in my new design I want to replace the relationship by using sparse columns. you Can see diagram below.

I know I would have Redundancy.but i want to know what is the other risk of this way of design? by this new way my queries would be very easy and fast.what is your idea about it?sorry for my bad english,and thanks.

Answer 1

If there would be only one entry per wfdoc.id in the three satellite tables (attendance, credit, replacedetail), then your new design is possible, although wasteful of disk space. But if there could be several entries in the attendance table for one wfdoc.id, then this is a very bad idea.