Here's some C to use to create the operator classes, seems to work ok.
---
#include "postgres.h"
#include <string.h>
#include "fmgr.h"
#include "utils/date.h"
/* For date sorts */
PG_FUNCTION_INFO_V1(ddd_date_revcmp);
Datum ddd_date_revcmp(PG_FUNCTION_ARGS){
DateADT arg1=PG_GETARG_DATEADT(0);
DateADT arg2=PG_GETARG_DATEADT(1);
PG_RETURN_INT32(arg2 - arg1);
}
/* For integer sorts */
PG_FUNCTION_INFO_V1(ddd_int_revcmp);
Datum ddd_int_revcmp(PG_FUNCTION_ARGS){
int32 arg1=PG_GETARG_INT32(0);
int32 arg2=PG_GETARG_INT32(1);
PG_RETURN_INT32(arg2 - arg1);
}
/* For string sorts */
PG_FUNCTION_INFO_V1(ddd_text_revcmp);
Datum ddd_text_revcmp(PG_FUNCTION_ARGS){
text* arg1=PG_GETARG_TEXT_P(0);
text* arg2=PG_GETARG_TEXT_P(1);
PG_RETURN_INT32(strcmp((char*)VARDATA(arg2),(char*)VARDATA(arg1)));
}
/*
create function ddd_date_revcmp(date,date) returns int4 as
'/data/postgres/contrib/cmplib.so', 'ddd_date_revcmp' LANGUAGE C STRICT;
create function ddd_int_revcmp(int4,int4) returns int4 as
'/data/postgres/contrib/cmplib.so', 'ddd_int_revcmp' LANGUAGE C STRICT;
create function ddd_text_revcmp(text,text) returns int4 as
'/data/postgres/contrib/cmplib.so', 'ddd_text_revcmp' LANGUAGE C STRICT;
*/
----- Original Message -----
From: "Stephan Szabo" <sszabo@xxxxxxxxxxxxxxxxxxxxx>
To: <J@xxxxxxxxxxx>
Sent: Wednesday, January 18, 2006 2:24 PM
Subject: Re: [PERFORM] Multiple Order By Criteria
On Wed, 18 Jan 2006 J@xxxxxxxxxxx wrote:
Could you explain to me how do create this operator class for a text data
type ? I think it will give me more of an understanding of what's going
on
if I could see this example.
Using an SQL function (mostly because I'm too lazy to look up the C call
syntax) I think it'd be something like:
create function bttextrevcmp(text, text) returns int4 as
'select bttextcmp($2, $1)' language 'sql';
CREATE OPERATOR CLASS text_revop
FOR TYPE text USING btree AS
OPERATOR 1 > ,
OPERATOR 2 >= ,
OPERATOR 3 = ,
OPERATOR 4 <= ,
OPERATOR 5 < ,
FUNCTION 1 bttextrevcmp(text,text);
I believe bttextcmp is the standard text btree operator class helper
function, so we call it with reverse arguments to try to flip its results
(I think -bttextcmp($1,$2) would also work).
