نحوه نوشتن پسوندهای PostgreSQL در C++

factorial_extension/
    |
    +-- factorial_extension.control
    |
    +-- factorial_extension.cpp
    |
    +-- factorial_extension--1.0.sql
    |
    +-- Makefile

#include <postgres.h>
#include <fmgr.h>
#include <utils/numeric.h>

#ifdef PG_MODULE_MAGIC
PG_MODULE_MAGIC;
#endif

extern "C" {
    PG_FUNCTION_INFO_V1(factorial);

    Datum factorial(PG_FUNCTION_ARGS) {
        int32 arg = PG_GETARG_INT32(0);

        if (arg < 0)
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                     errmsg("Factorial input must be a non-negative integer")));

        int64 result = 1;
        for (int i = 2; i <= arg; ++i)
            result *= i;

        PG_RETURN_INT64(result);
    }
}

# factorial_extension.control
comment="Extension to calculate factorial"
default_version = '1.0'
module_pathname="$libdir/factorial_extension"
relocatable = false

-- factorial_extension--1.0.sql

-- Create the extension schema
CREATE SCHEMA factorial_extension;

-- Create the SQL function
CREATE OR REPLACE FUNCTION factorial_extension.factorial(integer)
RETURNS bigint AS 'factorial_extension', 'factorial'
LANGUAGE C STRICT;

-- Grant execute permission to public (change to appropriate roles if needed)
GRANT EXECUTE ON FUNCTION factorial_extension.factorial(integer) TO PUBLIC;

MODULES = factorial_extension
PG_CONFIG = pg_config
PGXS := $(shell $(PG_CONFIG) --pgxs)
include $(PGXS)

CREATE EXTENSION factorial_extension;

SELECT factorial_extension.factorial(5);