This topic is discussed again and again with huge friend of mine and MySQL sectarian. 🙂 And must confess I agree with him in this particular point of view.
For me it’s strange that such powerful database as PostgreSQL, which has a lot of drums and whistles inside, doesn’t support SET types. Especially when we have ENUM support now!
Of course one may say that this functionality can be implemented using Bit String Types. But where is the joy of power? Where is the crystal clarity of the SQL script? 🙂
What’s you opinion, postgresman?
PS Don’t hesitate to share your thoughts in the comments.
Pasha Golub's Blog 
I assume by “set” you mean “just like an array but unordered and without duplicates” or “just like a unary relation”. So, a “set” type is useful just as a shorthand or more efficient implementation of said.
But if by “set” you mean “pick multiple values from an enumerated list”, then I would say just do what I said in the first paragraph and people can use an enumerated type as the element type of the set rather than say integer or text or whatever.
LikeLike
I’m not sure that treat you right. 🙂
A set is a collection of values of the same ordinal type (enums, integers). The values have no inherent order, nor is it meaningful for a value to be included twice in a set.
LikeLike
Yes, a set is an unordered collection of values with each value only appearing once.
But a better, more general solution is to just support nesting relations in relations. Which MULTISET essentially does, though in a more contrived manner by having different operators for MULTISET as for base tables.
LikeLike
I’m not against MULTISET, but support for simple SET is trivial, as for me. It’s matter of time and effort.
LikeLike
If we’re going to get something, why not MULTISET, which is in the standard?
LikeLike
Cool! Never heard about this. I think MULTISET is much better, but from other hand is much more complicated.
LikeLike
It seems to me that developers of a database system would mimic the popular functionality of their competitor’s products almost as a matter of course.. If customers want something, and it doesn’t break something else or otherwise cause serious problems, then they should get it. Otherwise they’ll find a database vendor who will give it to them.
LikeLike