My english is not perfect, by accumulative i think about monotonically increasing function.
It works that for clause WHERE f(x)=const: 1. Read root page of index_on_x and get x1 ... Xn 2. Calculate f(x1) ... f(xn) for this page 3. When f(x1)<=const<= f(xn) then x1 <= searched x <= xn and we can test smaller range (xlower, xgreater). 4. Otherwise no rows satisfy condition. Step 3 we repeat for current index's page and subpages until xlower = searched x = xgreater 2011/9/25, Tom Lane <t...@sss.pgh.pa.us>: > =?ISO-8859-2?Q?pasman_pasma=F1ski?= <pasma...@gmail.com> writes: >> I propose to add "accumulative" flag to a function definition. This >> flag would be set for function f(x) which is accumulative and >> immutable. > > Maybe you'd better define what you mean by "accumulative" ... > >> This flag allows to use an index on x for clauses containing f(x): >> where f(x) = const >> where f(x) > const > > ... because it's sure not clear how you would get that to work. > > regards, tom lane > -- ------------ pasman -- Sent via pgsql-general mailing list (pgsql-general@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
