I found second use case. Look at expression: where left(str,n)='value' function left(str,n) increase monotonically for str and n. With this feature it can use index on str. Classic index needs recreating. 2011/9/25, Pavel Stehule <pavel.stehule@xxxxxxxxx>: > Hello > > what is a real use case? > > Regards > > Pavel > > 2011/9/25 pasman pasmański <pasman.p@xxxxxxxxx>: >> 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 <tgl@xxxxxxxxxxxxx>: >>> =?ISO-8859-2?Q?pasman_pasma=F1ski?= <pasman.p@xxxxxxxxx> 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@xxxxxxxxxxxxxx) >> To make changes to your subscription: >> http://www.postgresql.org/mailpref/pgsql-general >> > -- ------------ pasman -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
