Re: How to compare different datums within from a tuple?

Am 11.08.2015 um 13:41 schrieb Anastasia Lubennikova:
> Can someone tell me, how I can compare two datum fields, when I do
> not know the data type in advance inside an executor function?
>
>
> In a nutshell, there is no way to compare Datums.
> Datum is an abstact data type. It's the backend internal representation
> of a single value of any SQL data type.
> The code using Datum has to know which type it is, since the Datum
> itself doesn't contain that information.
>
> For example, "x less than y" where x and y are of various types that
> form intervals. I have found the method ExecTuplesMatch, but it is
> only for equality comparison, I think. Another one is
> ApplySortComparator... maybe that's the correct way to go?
>
> Some code to make things clearer...
>
> Datum x = heap_getattr(out->tts_tuple,
> node->xpos,
> out->tts_tupleDescriptor,
> &isNull1);
> Datum y = slot_getattr(curr, node->ypos, &isNull2);
>
> if (compareDatumWithCorrectMethod(x,y) < 0)
> {
> /* do something */
> }
>
> Thx,
> Peter
>
>
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>
> Maybe you can use DatumGetXXX function to extract value. For example,
> DatumGetInt32.
> <http://doxygen.postgresql.org/postgres_8h.html#aacbc8a3ac6d52d85feaf0b7ac1b1160c>
> --
> Best regards,
> Lubennikova Anastasia

I did this with another column, that has always the result of
row_number() as content, which I think will be fine when I use
DatumGetInt32.

Thanks,
Peter