Re: Null row vs. row of nulls in plpgsql

I assume this is a TODO, right?

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Tom Lane wrote:
> I looked a bit at the bug report here:
> http://archives.postgresql.org/pgsql-bugs/2008-09/msg00164.php
>
> ISTM that the fundamental problem is that plpgsql doesn't distinguish
> properly between a null row value (eg, "null::somerowtype") and a
> row of null values (eg, "row(null,null,...)::somerowtype"). When that
> code was designed, our main SQL engine was pretty fuzzy about the
> difference too, but now there is a clear semantic distinction.
>
> For plpgsql's RECORD variables this doesn't seem hard to fix: just
> take out the code in exec_move_row() that manufactures a row of nulls
> when the input is null, and maybe make a few small adjustments
> elsewhere. For ROW variables there's a bigger problem, because those
> are represented by a list of per-field variables, which doesn't
> immediately offer any way to represent overall nullness. I think it
> could be dealt with by adding an explicit "the row as a whole is null"
> flag to struct PLpgSQL_row. I haven't tried to code it though, so I'm
> not sure if there are gotchas or unreasonably large code changes needed
> to make it happen.
>
> I thought for a little bit about whether we couldn't get rid of ROW
> variables entirely, or at least make them work more like RECORD variables
> by storing a HeapTuple instead of a list of per-field variables. But
> I soon found out that the reason to have them is to be able to describe
> the assignment target of SQL statements that assign to multiple scalar
> variables, eg "SELECT ... INTO x,y,z".
>
> Comments?
>
> regards, tom lane
>
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Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com

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