Hi
i have an ordered table of dates let's
say:
1/1/2004
8/1/2004
15/1/2004
29/1/2004
5/2/2004
12/2/2004
I am searching for a way to have the minimum date
and maximum date for dates seperated by one week whitout gaps between
them in a string.
which will give the
following output:
1/1/2004:15/1/2004;29/1/2004:12/2/2004;
I was thinking of doing this with an aggregate function.
So i thought about writing the following C code :
#include "postgres.h"
#include "utils/date.h"
int32 i;//initially equal to zero
text * charresult;
/*
text * concat(,){} // NOT IMPLEMENTED (HOW TO DO IT ??)
*/
PG_FUNCTION_INFO_V1(computechar);
Datum computechar(PG_FUNCTION_ARGS) {
DateADT
d1=PG_GETARG_DATEADT(0);
DateADT d2=PG_GETARG_DATEADT(1);
int32 diff=
(int32) (d2 -
d1);
i++;
if(diff == 7*i)
PG_RETURN_DATEADT(d1);
else
{
charresult=concat(charresult,d1);
charresult=concat(charresult,":");
charresult=concat(charresult,d2);
charresult=concat(charresult,";");
PG_RETURN_DATEADT(d2);
}
}
PG_FUNCTION_INFO_V1(returncomputedchar);
Datum returncomputedchar (PG_FUNCTION_ARGS) {
PG_RETURN_TEXT_P(charresult);
}
And then i will create the aggregate as follows (after compiling
...) :
CREATE OR REPLACE FUNCTION computechar(date,date) returns date as
'/home/nabifadel/tempo/groupingWeeks.so' LANGUAGE 'C' WITH (isStrict);
CREATE OR REPLACE FUNCTION returncomputedchar (date) returns text as
'/home/nabifadel/tempo/groupingWeeks.so' LANGUAGE 'C' WITH (isStrict);
CREATE AGGREGATE groupe_weeks_agg( basetype = date, sfunc =
computechar,stype = date, finalfunc = returncomputedchar);
The function 'computechar' will put the result in the variable
'charresult' that will be returned by the function 'returncomputedchar'.
My first question is : Could this work the way i am thinking of it
??
My second question is how to implement the function 'concat' that
will return a text concatenation of dates and text.
(the question is basically how to transform a date into
text).
It's the first time i try to implement an aggregate function and i need
help + i haven't been using C language frequently the last few years
(there may be errors) .
Thx.
