On 2016/06/24 15:44, Ashutosh Bapat wrote: >> >> I think the proposed idea of applying record::text explicit coercion to a >> whole-row reference in the IS NOT NULL condition in the CASE WHEN >> conversion would work as expected as you explained, but I'm concerned that >> the cost wouldn't be negligible when the foreign table has a lot of columns. > > That's right, if the foreign server doesn't optimize the case for IS NOT > NULL, which it doesn't :) > > I am happy to use any cheaper means e.g a function which counts number of > columns in a record. All we need here is a way to correctly identify when a > record is null and not null in the way we want (as described upthread). I > didn't find any quickly. Do you have any suggestions?
I'm now starting to wonder if it would be outright wrong to just use the alias names of corresponding foreign tables directly for whole-row references? So, instead of these in target lists of remote queries:
SELECT CASE WHEN (r1.*)::text IS NOT NULL THEN ROW (r1.*) END, ...
This is wrong. The deparsed query looks like SELECT CASE WHEN (r1.*)::text IS NOT NULL THEN ROW (r1.col1, r1.col2, ...) END,
The reason for this is that the foreign table definition may not match the target table definition. This has been explained in the comments that you have deleted in your patch. Am I missing something?
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Best Wishes, Ashutosh Bapat EnterpriseDB Corporation The Postgres Database Company
