RE: Query ID Calculation Fix for DISTINCT / ORDER BY and LIMIT / OFFSET

Hello, David!

As I can see, your patch has the same idea as my v2-0001-Query-ID-Calculation-Fix-Variant-B.patch from [1]. 
I think it would be better to extract the jumble buffer update with hash calculation into a function
(CompressJumble in my patch). This will result in fewer changes to the source code. 
We can also simply dump the null count to the buffer when we encounter a non-null field
(which will be processed in AppendJumble, indeed).

What do your thing about my patch (v2-0001-Query-ID-Calculation-Fix-Variant-B.patch)?

[1] https://www.postgresql.org/message-id/5ac172e0b77a4baba50671cd1a15285f%40localhost.localdomain