C++ 如何编写postgresql支持函数

我正在try 用PostgreSQL编写一个支持函数来设置 Select 性.

我有一个功能

PG_FUNCTION_INFO_V1(pgq3c_sindist_5);
Datum pgq3c_sindist_5(PG_FUNCTION_ARGS)

我希望有一个辅助功能来设定 Select 性. 函数pgq3c_sindist_5返回布尔值，我有一个 支持功能

PG_FUNCTION_INFO_V1(pgq3c_join_selectivity);
Datum pgq3c_join_selectivity(PG_FUNCTION_ARGS)
{
  Node    *rawreq = (Node *) PG_GETARG_POINTER(0);
  Node    *unknown = (Node *) PG_GETARG_POINTER(1);
  Node    *ret = NULL;
  Datum radDatum;
  double rad;
 if (IsA(rawreq, SupportRequestSelectivity))
    {
      SupportRequestSelectivity *req = (SupportRequestSelectivity *) rawreq;

      radDatum = llast_node(Datum,req->args);
      rad = DatumGetFloat8(radDatum);


      elog(WARNING,"rad = %lf",rad);

      /* I would like to make the selectivity a function of rad */
      req->selectivity = 0.05;
      ret = (Node *) req;
    }

我的非支持函数有五个参数.我希望我的支持功能 在我的支持中使用第五个参数pgq3c_sindist_5 功能.我的代码不转储代码，但我的rad总是以0.0结尾， 当我百分之百确定我没有将零作为我的任何参数传递时 我的主要职能.

如果我对源代码的理解是正确的，那么SupportRequestSelectivity具有 的

/* Input fields: */
struct PlannerInfo *root;   /* Planner's infrastructure */
Oid         funcid;         /* function we are inquiring about */
List       *args;           /* pre-simplified arguments to function */
Oid         inputcollid;    /* function's input collation */
bool        is_join;        /* is this a join or restriction case? */
int         varRelid;       /* if restriction, RTI of target relation */
JoinType    jointype;       /* if join, outer join type */
struct SpecialJoinInfo *sjinfo; /* if outer join, info about join */

由此，我认为List*args应该是我的main函数的参数， 我应该能够解析这个.

我完全找错人了吗？

我想要在我的Support函数中找到Main函数的参数的值.

编辑:我的新代码看起来像

PG_FUNCTION_INFO_V1(pgq3c_join_selectivity);
Datum pgq3c_join_selectivity(PG_FUNCTION_ARGS)
{
  Node    *rawreq = (Node *) PG_GETARG_POINTER(0);
  Node    *ret = NULL;
  Datum radDatum;
  double rad;
  double ratio;
  Node *dummy = NULL;
  
  if (IsA(rawreq, SupportRequestSelectivity))
    {
      SupportRequestSelectivity *req = (SupportRequestSelectivity *) rawreq;
      Selectivity s1;
      
      dummy = (Node *) lfirst(list_nth_cell(req->args, 4));

      if (IsA(dummy,Const))
    {
      Const *con = (Const *) dummy;
      radDatum = PointerGetDatum(con->constvalue);
      rad = DatumGetFloat8(radDatum);     
      ratio = 3.14 * rad * rad / 41252.;  /* pi*r^2/whole_sky_area */
      /* clamp at 0, 1*/
      CLAMP_PROBABILITY(ratio);
      //elog(WARNING, "HERE0.... %e", ratio);
      req->selectivity = ratio;
      ret = (Node *) req;
    }
    }
  if (IsA(rawreq, SupportRequestSimplify))
    {
      SupportRequestSimplify *req = (SupportRequestSimplify *) rawreq;      
      PG_RETURN_POINTER((Node *)0);
    }
  if (IsA(rawreq, SupportRequestCost))
    {
      elog(WARNING,"found SupportRequestCost");
      /* Provide some generic estimate */
      SupportRequestCost *req = (SupportRequestCost *) rawreq;

      /* not yet implemented */
      
      ret = (Node *) req;
    }
  PG_RETURN_POINTER(ret);
}