Re: what is the meaning of Datum?

Excerpts from Luca Ferrari's message of mié jun 23 06:09:28 -0400 2010:
> Hi all,
> ok this is a silly question, but I've got a doubt: what is the exact meaning 
> of Datum? I see having a look at the macroes (e.g., PG_RETURN_XXX) that a 
> Datum can be used as a pointer or as a single data, that is it can be a 
> reference or a value. Is this right?

Yes

> So for instance the fact that each stored 
> procedure returns a Datum means that the semantic of the Datum is interpreted 
> depending on how the procedure is defined in the SQL language (i.e., it returns 
> a integer, a tuple, ...). Am I right?

Yes

> Moreover, is there a documentation (aside the source code) that explains and 
> links each internal data structure like HeapTuple, HeapTupleHeader, and so on?

The source code comments should be plenty.  Have you tried reading
those?

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Álvaro Herrera 
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