Re: [PROPOSAL] Covering + unique indexes.

CREATE INDEX ... ON table (f1, f2, f3) UNIQUE(f1, f2) INCLUDE(f4);

I don't see an advantage this form. What is f3 column? just order? and f4 will not be used for compare?  At least now it requires additional checks that UNIQUE() fields are the same as first columns in definition. Non ordering field f4 will  require invasive intervention in planner because now it believes that all columns in btree are ordered.       

I agree, that form
CREATE UNIQUE INDEX i ON t (f1, f2, f3) INCLUDE (f4)
is clear. f4 will be used in row compare and actually planner will be able to use it as unique index (f1, f2, f3) with additional f4 or as
as unique index (f1, f2, f3, f4), because uniqueness on (f1, f2, f3) gives warranty of uniqueness on (f1, f2, f3, f4)