example of aggregate function for product
I needed to write a product aggregate function, and just happened to
find this example in the nodes to the 8.0 manual:
Ansis <ansis_no_ AT inbox.lv>13 Jan 2006 16:41:05
An aggregate multiplication function, an analog of "sum" (the same
should be defined also for other numeric types):
CREATE OR REPLACE FUNCTION mul2(FLOAT,FLOAT)
RETURNS FLOAT AS '
DECLARE
a ALIAS FOR $1;
b ALIAS FOR $2;
BEGIN
RETURN a*b;
END;
' LANGUAGE plpgsql;
CREATE AGGREGATE mul (
sfunc = mul2,
basetype = FLOAT,
stype = FLOAT,
initcond = '1'
);
but that example looks pretty different than the ones found in the 8.3
manual (avg for instance):
CREATE AGGREGATE avg (float8)
(
sfunc = float8_accum,
stype = float8[],
finalfunc = float8_avg,
initcond = '{0,0}'
);
and float8_accum is defined like this (in the postgres function list).
CREATE OR REPLACE FUNCTION float8_accum(double precision[], double precision)
RETURNS double precision[] AS
'float8_accum'
LANGUAGE 'internal' IMMUTABLE STRICT
COST 1;
ALTER FUNCTION float8_accum(double precision[], double precision)
OWNER TO postgres;
COMMENT ON FUNCTION float8_accum(double precision[], double precision)
IS 'aggregate transition function';
Are there any experts out there who have defined a product or
cumulative product function that abides best practices who would be
willing to share?
Thanks,
Whit
Whit Armstrong escribi�:
Ansis <ansis_no_ AT inbox.lv>13 Jan 2006 16:41:05
An aggregate multiplication function, an analog of "sum" (the same
should be defined also for other numeric types):CREATE OR REPLACE FUNCTION mul2(FLOAT,FLOAT)
RETURNS FLOAT AS '
DECLARE
a ALIAS FOR $1;
b ALIAS FOR $2;
[...]
but that example looks pretty different than the ones found in the 8.3
manual (avg for instance):
The main difference is that the 8.3 docs example piggybacks on C
language functions that you must compile and install separately, whereas
the comment function uses a plpgsql function and is self-contained.
Other than that (and the fact that the second one is for averages not
multiplication), both examples are technically identical ...
--
Alvaro Herrera http://www.CommandPrompt.com/
The PostgreSQL Company - Command Prompt, Inc.
Whit Armstrong wrote:
I needed to write a product aggregate function, and just happened to
find this example in the nodes to the 8.0 manual:
[...]
but that example looks pretty different than the ones found in the 8.3
manual (avg for instance):
[...]
Are there any experts out there who have defined a product or
cumulative product function that abides best practices who would be
willing to share?
I don't know what "best practices" are, but the following works
fine on PostgreSQL 8.3 and 8.4:
CREATE AGGREGATE mul(double precision) (SFUNC=float8mul, STYPE=double precision, INITCOND=1);
Yours,
Laurenz Albe