Almost there.

As suggested by Fabian in the following thread I gave up the MX file approach and implemented group_concat as UDF in C.

When I try to conclude my function UDFBATgroup_concat_(BAT **ret, BAT *b, BAT *g, BAT *h, FILE* fp) //ignore fp

as follows:

BATaccessBegin(h, USE_HEAD | USE_TAIL, MMAP_SEQUENTIAL);

index = 0;

BATloop(h, p, q)

{

ptr hhead = BUNhead(hi, p);

fprintf(fp, "%d: hhead=%d", index, hhead);

str dst = tailValArray[index];

fprintf(fp, "%d: dstStr=%s# ", index, dst);

BUNins(bn, hhead, dst, FALSE);

fprintf(fp, "%d: Insert complete\n", index);

index++;

}

I get the following error on the client terminal

[tapomay@tapomay-laptop monetdata]$ echo "select house, group_concat(name) from gs group by house;" | mclient -d tapomay

GDKerror:!ERROR: BUNins: access denied to tmp_10162, aborting.

BUNins: access denied to tmp_10162, aborting.

The groupings are ready in the tailVarArray.

NEED HELP.

Thanks and Regards,

Tapomay.