data modeling

Under what circumstances that a table should reference/link to itself? I 've seen ppl do that. Is it a good practice to have that kinda of design?

And also how much of a performance sacrify when a query involving joining 2 or more tables, compare to a single table inqury?

any input is appreciated. thanks

-Ken Received on Wed Oct 31 2001 - 00:32:13 CST