Re: To know what a macro does - Mailing list pgsql-hackers

Well, I do a query like this: "SELECT * FROM historial WHERE id_grupo=grupo_hist ORDER BY grmemb LIMIT 10;", then in transformSortClause I know it this way:

 /*
 * transformSortClause -
 *      transform an ORDER BY clause
 *
 * ORDER BY items will be added to the targetlist (as resjunk columns)
 * if not already present, so the targetlist must be passed by reference.
 */
List *
transformSortClause(ParseState *pstate,
                    List *orderlist,
                    List **targetlist,
                    bool resolveUnknown)
{
    List       *sortlist = NIL;
    ListCell   *olitem;

    foreach(olitem, orderlist)
    {
        SortBy       *sortby = lfirst(olitem);
        TargetEntry *tle;
        //To find out if it is the membership degree
        char       *namegrmemb = strVal(linitial(((ColumnRef *) sortby->node)->fields));

        if (strcmp(namegrmemb, "grmemb")==0)
            tle = createTargetFuzzyEntry(targetlist);
        else
            tle = findTargetlistEntry(pstate, sortby->node,
                                      targetlist, ORDER_CLAUSE);

        sortlist = addTargetToSortList(pstate, tle,
                                       sortlist, *targetlist,
                                       sortby->sortby_dir,
                                       sortby->sortby_nulls,
                                       sortby->useOp,
                                       resolveUnknown);
       
       

    }

    return sortlist;
}

|***************************************************************************************************************************|

Then I created a function that includes a new target entry in the targetlist:

//To sort the membership degree
TargetEntry *
createTargetFuzzyEntry(List **targetlist){
   
    /*I just have to create the fuzzy target entry right here */
    TargetEntry    *tfp = makeNode(TargetEntry);
    Const   *cn = makeNode(Const);
    float    val = 1.0;
    TargetEntry *tlast = list_nth(*targetlist, list_length(*targetlist)-1);

    cn = makeConst(700, -1, 4, (Float4GetDatum(val)), false, true);
    tfp->resorigtbl=tlast->resorigtbl;
    tfp->expr = (Expr *) cn;
    tfp->resno = list_length(*targetlist) + 1;
    tfp->resname = "grmemb";
    tfp->resorigcol = list_length(*targetlist) + 1;
    tfp->ressortgroupref = 0;
    tfp->resjunk = false;

    *targetlist = lappend(*targetlist, tfp);

    return tfp;
}

|*************************************************************************************************************************|

Later in planner.c on grouping_planner function I do something like this:

/*
     * If we were not able to make the plan come out in the right order, add
     * an explicit sort step.
     */
    if (parse->sortClause)
    {
        if (!pathkeys_contained_in(sort_pathkeys, current_pathkeys) || parse->hasGrMemb)
        {
            result_plan = (Plan *) make_sort_from_pathkeys(root,
                                                           result_plan,
                                                           sort_pathkeys,
                                                           limit_tuples);
            current_pathkeys = sort_pathkeys;
        }
    }