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

>
> 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