"Nick Fankhauser" <nickf(at)ontko(dot)com> writes:
> So is a multi-column index really just two separate indexes with a
> constraint added if necessary? I guess I had an idea in my head that it
> would be something like an index on the concatenation of the two fields.
Well, it *is* an index on the concatenation of the fields --- but you
can perfectly well use that to search for values of the first field.
(You can't use it to search for values of the second field without
the first, however.)
regards, tom lane