Re: WIP: generalized index constraints

On Tue, 2009-07-07 at 13:22 -0400, Tom Lane wrote:
> ALTER TABLE tab ADD CONSTRAINT UNIQUE (col1, col2) USING index

This would be very useful, though perhaps only because we do not have
REINDEX CONCURRENTLY.

It is likely to be useful in the future to allow an index with N
columns, yet which can provide uniqueness with < N of those columns.
This capability is known as covered indexes and will be important if
Heikki writes his index-only scan code.

-- Simon Riggs           www.2ndQuadrant.comPostgreSQL Training, Services and Support