... When n changes of course. Sorry for top posting, phone not allows to move cite. 2011/9/25, pasman pasmański <pasman.p@xxxxxxxxx>: > 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 > -- ------------ pasman -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
