Example: my_sum Definition

my_sum definition

Since my_sum, like SUM, can be used in any context, all the optimized optional entry points have been supplied. In this example, the normal _evaluate_extfn function can also be used as the _evaluate_superaggregate_extfn function.

#include "extfnapiv4.h"
#include <stdlib.h>
#include <assert.h>


//  Simple aggregate UDF that adds up a set of 
//  integer arguments, and whenever asked returns 
//  the resulting big integer total.  For int
//  arguments, the only difference between this
//  UDF and the SUM built-in aggregate is that this
//  UDF will return NULL if there are no input rows.
//
//  The start function creates a little structure for
//  the running total, and the finish function then
//  deallocates it.
//
//  Since there are no aggregate usage restrictions 
//  for this aggregate UDF, the corresponding SQL declaration
//  will look like:
//
//              CREATE AGGREGATE FUNCTION my_sum(IN arg1 INT) 
//                      RETURNS BIGINT
//                      ON EMPTY INPUT RETURNS NULL
//                      EXTERNAL NAME 'my_integer_sum@libudfex'


typedef struct my_total {
  a_sql_int64   _total;
  a_sql_uint64  _num_nonnulls_seen;
} my_total;


extern "C"
void my_integer_sum_start(a_v3_extfn_aggregate_context *cntxt)
{
}


extern "C"
void my_integer_sum_finish(a_v3_extfn_aggregate_context *cntxt)
{
}


extern "C"
void my_integer_sum_reset(a_v3_extfn_aggregate_context *cntxt)
{
  my_total *cptr = (my_total *)cntxt->_user_calculation_context;
  cptr->_total = 0;
  cptr->_num_nonnulls_seen = 0;
}


extern "C"
void my_integer_sum_next_value(a_v3_extfn_aggregate_context *cntxt, 
                               void *arg_handle)
{
  an_extfn_value  arg;
  a_sql_int32 arg1;

  my_total *cptr = (my_total *)cntxt->_user_calculation_context;

  //  Get the one argument, and if non-NULL then add it to the total
  //
  if (cntxt->get_value( arg_handle, 1, &arg) && arg.data) {
    arg1 = *((a_sql_int32 *)arg.data);
    cptr->_total += arg1;
    cptr->_num_nonnulls_seen++;
  }
}


extern "C"
void my_integer_sum_drop_value(a_v3_extfn_aggregate_context *cntxt, 
                               void *arg_handle)
{
  an_extfn_value  arg;
  a_sql_int32 arg1;
  my_total *cptr = (my_total *)cntxt->_user_calculation_context;

  //  Get the one argument, and if non-NULL then subtract it from the total
  if (cntxt->get_value( arg_handle, 1, &arg) && arg.data) {
    arg1 = *((a_sql_int32 *)arg.data);
    cptr->_total -= arg1;
    cptr->_num_nonnulls_seen--;
  }
}


extern "C"
void my_integer_sum_evaluate(a_v3_extfn_aggregate_context *cntxt, 
                             void *arg_handle)
{
  an_extfn_value  outval;
  my_total *cptr = (my_total *)cntxt->_user_calculation_context;

  //  Set the output result value.  If the inputs
  //  were all NULL, then set the result as NULL.
  //
  outval.type = DT_BIGINT;
  outval.piece_len = sizeof(a_sql_int64);
  if (cptr->_num_nonnulls_seen > 0) {
    outval.data = &cptr->_total;
  } else {
    outval.data = 0;
  }
  cntxt->set_value( arg_handle, &outval, 0 );
}


extern "C"
void my_integer_sum_cum_evaluate(
                        a_v3_extfn_aggregate_context *cntxt, 
                        void *arg_handle)
{
  an_extfn_value  outval;
  an_extfn_value  arg;
  int arg1;
  my_total *cptr = (my_total *)cntxt->_user_calculation_context;

  //  Get the one argument, and if non-NULL then add it into the total.
  //
  if (cntxt->get_value( arg_handle, 1, &arg) && arg.data) {
    arg1 = *((a_sql_int32 *)arg.data); 
    cptr->_total += arg1;
    cptr->_num_nonnulls_seen++;
  }

  //  Then set the output result value.  If the inputs
  //  were all NULL, then set the result as NULL.
  //
  outval.type = DT_BIGINT;
  outval.piece_len = sizeof(a_sql_int64);
  if (cptr->_num_nonnulls_seen > 0) {
    outval.data = &cptr->_total;
  } else {
    outval.data = 0;
  }
  cntxt->set_value( arg_handle, &outval, 0 );
}


extern "C"
void my_integer_sum_next_subagg_value(
                a_v3_extfn_aggregate_context *cntxt, 
                void *arg_handle)
{
  an_extfn_value  arg;
  a_sql_int64 arg1;

  my_total *cptr = (my_total *)cntxt->_user_calculation_context;

  //  Get the one argument, and if non-NULL then add it to the total
  //
  if (cntxt->get_value( arg_handle, 1, &arg) && arg.data) {
    arg1 = *((a_sql_int64 *)arg.data);
    cptr->_total += arg1;
    cptr->_num_nonnulls_seen++;
  }
}


extern "C"
void my_integer_sum_drop_subagg_value(
                a_v3_extfn_aggregate_context *cntxt, 
                void *arg_handle)
{
  an_extfn_value  arg;
  a_sql_int64 arg1;

  my_total *cptr = (my_total *)cntxt->_user_calculation_context;

  //  Get the one argument, and if non-NULL then subtract it from the total
  //
  if (cntxt->get_value( arg_handle, 1, &arg) && arg.data) {
    arg1 = *((a_sql_int64 *)arg.data);
    cptr->_total -= arg1;
    cptr->_num_nonnulls_seen--;
  }
}



a_v3_extfn_aggregate my_integer_sum_descriptor = 
{ 
        &my_integer_sum_start, 
        &my_integer_sum_finish,
        &my_integer_sum_reset,
        &my_integer_sum_next_value,
        &my_integer_sum_evaluate,
        &my_integer_sum_drop_value,
        &my_integer_sum_cum_evaluate,
        &my_integer_sum_next_subagg_value,
        &my_integer_sum_drop_subagg_value,
        &my_integer_sum_evaluate,
        NULL, // reserved1_must_be_null
        NULL, // reserved2_must_be_null
        NULL, // reserved3_must_be_null
        NULL, // reserved4_must_be_null
        NULL, // reserved5_must_be_null
        0, // indicators
        ( short )sizeof( my_total ), // context size
        8, // context alignment
        0.0, //external_bytes_per_group 
        0.0, // external bytes per row
        0, // reserved6_must_be_null
        0, // reserved7_must_be_null
        0, // reserved8_must_be_null
        0, // reserved9_must_be_null
        0, // reserved10_must_be_null
        NULL // _for_server_internal_use
};

extern "C"
a_v3_extfn_aggregate *my_integer_sum()
{
  return &my_integer_sum_descriptor;
}