Re: support for MERGE

On 2022-Jan-17, Japin Li wrote:

> So for NOT MATCHED, we are expected not use the target table columns.
>
> The code comes from execMerge.c says:
>
> /*
> * Make source tuple available to ExecQual and ExecProject. We don't need
> * the target tuple, since the WHEN quals and the targetlist can't refer to
> * the target columns.
> */
> econtext->ecxt_scantuple = NULL;
> econtext->ecxt_innertuple = slot;
> econtext->ecxt_outertuple = NULL;
>
> It will set econtext->ecxt_scantuple to NULL, which leads the crash.

Right. So this was broken by the fact that I recently allowed MATCHED
actions to target DO NOTHING; previously, only NOT MATCHED actions could
do so. So the bug was present, but it wasn't accessible.

> Should we setNamespaceVisibilityForRTE() for CMD_NOTHING? I try to set it
> and it works as expected. OTOH, the system attributes from target table
> also cannot be accessible. I'm not sure the v6 patch how to implement this
> limitation.

I changed this block so that it depends on whether the clause is MATCHED
or NOT MATCHED, rather than the action. I think it was pretty
nonsensical for it to be keyed on action type, and it made the code
needlessly longer.

Thank you!

--
Álvaro Herrera Valdivia, Chile — https://www.EnterpriseDB.com/
"All rings of power are equal,
But some rings of power are more equal than others."
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