[C++] OrderBy SelectK does not display non-empty results #38633

Describe the bug, including details regarding any error messages, version, and platform.

When limit k is greater than the actual table data and the table contains Null/NaN, the data cannot be obtained and only non-empty results are available.

for example:

select * from test;
 i | j 
---+---
   | 5
 1 | 3
 3 |  
   |  
 2 | 5
 1 | 5
 3 | 5
(7 rows)

When we execute order by limit k：

 i | j 
---+---
 1 | 3
 1 | 5
 2 | 5
 3 | 5
 3 |  
(5 rows)

Only 5 non-empty records will be returned.

Therefore, we support returning non-null and supporting the order of setting Null for each SortKey.

commit: 25fef20

Component(s)

C++