subselect removes rows

Hi there,

We recently ran into the following bug. Which is very annoying since you don't expect it to happen.

The bug is as follows:
When using certain commands in a sub-select, it removes the row.
This should never happen. It should return null instead. It worked in postgres 10, but somehow doesn't work anymore on postgres 13 (which we currently have)

Example query:

select

col1, col2, jsonb_each_text(col2)

from (

select 1 as col1, null::jsonb as col2

union all

select 1 as col1, '{"a":"2"}'::jsonb as col2

) t1

I haven't had the opportunity to test it on postgres 14, but I couldn't find anything about it in the release notes, so I don't expect it works any different in 14.

The workaround is obviously simple if we could use set returning functions in a case:
select
col1, col2,
case
when col2 is null then null
else jsonb_each_text(col2)
end
from (
select 1 as col1, null::jsonb as col2
union all
select 1 as col1, '{"a":"2"}'::jsonb as col2
) t1

but we can't.. so that kinda makes it problematic..

Can you please look into it?

Thanks,
Bas Poot

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