Re: single index on more than two coulumns a bad thing?

On Fri, Apr 02, 2004 at 01:00:45 +0200,
  Palle Girgensohn  wrote:
> 
> Is it always bad to create index xx on yy (field1, field2, field3);
> 
> I guess the problem is that the index might often grow bigger than the 
> table, or at least big enough not to speed up the queries?

One place where you need them in postgres is enforcing unique multicolumn
keys. These will get created implicitly from the unique (or primary key)
constraint. It isn't all that unusual to have a table that describes
a many to many (to many ...) relationship where the primary key is all
of the columns.