From: Alexey Nalbat <alexey@price.ru>
To: pgsql-interfaces@postgresql.org
Subject: Re: can external C-function get multiple rows?
Date: Fri, 27 Apr 2001 16:50:21 +0400
Message-ID: <01042718092204.12343@workshop.price.ru> (raw)
In-Reply-To: <16102.988296940@sss.pgh.pa.us>
References: <01042420581800.12729@workshop.price.ru>
<16102.988296940@sss.pgh.pa.us>
Tom, thank you very much.
I was succeeded in constructing such a test function. And now have another question.
I wrote function myarr(foo) which returns exactly 10 rows of random values in the range [0,foo).
But I also want this function to work correctly, when used in a query with limit clause, like
"select myarr(100) limit 6;". After a bit of experiments I supposed that while executing
this query postgres called myarr() seven times (not six!). And may be at the seven call
fcinfo has some_flag set to "stop_return", after checking which myarr() should do the same
as when returning 11's row with PG_RETURN_NULL and setting "isDone" to "ExprEndResult"
and resetting variables. Is it so? What are some_flag and "stop_return"?
Thanks in advance.
P.S.:
Now myarr() does not reset variables when "interrupted by limit", and because of this returns:
+++
+++
pl=# select myarr(100) limit 6;
?column?
----------
87
42
35
38
4
16
(6 rows)
pl=# select myarr(100) limit 6;
?column?
----------
69
9
40
(3 rows)
+++
+++
Here is myarr() code:
+++
+++
#include <stdlib.h>
#include "postgres.h"
#include "fmgr.h"
#include "nodes/execnodes.h"
#define N 10
int a_c[N];
int n_c=0;
int i_c=0;
PG_FUNCTION_INFO_V1(myarr);
Datum
myarr(PG_FUNCTION_ARGS)
{
int n=PG_GETARG_INT32(0);
if ( n_c!=n )
{
int j;
n_c=n;
i_c=0;
for ( j=0 ; j<N ; j++ )
{
a_c[j]=n_c*rand()/RAND_MAX;
}
}
if ( i_c<N )
{
i_c++;
((ReturnSetInfo*)fcinfo->resultinfo)->isDone=ExprMultipleResult;
PG_RETURN_INT32(a_c[i_c-1]);
}
else
{
n_c=0;
i_c=0;
((ReturnSetInfo*)fcinfo->resultinfo)->isDone=ExprEndResult;
PG_RETURN_NULL();
}
}
+++
+++
--
WBR, Alexey Nalbat
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Subject: Re: can external C-function get multiple rows?
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