[GitHub] [arrow-datafusion] izveigor commented on pull request #6662: feat: support `NULL` in array functions

["izveigor (via GitHub)" <gi...@apache.org>]

izveigor commented on PR #6662:
URL: https://github.com/apache/arrow-datafusion/pull/6662#issuecomment-1604650455

   Hello, @alamb!
   I am well aware of your arguments about NULL handling in arrays and initially agreed with it.
   But I found a serious problem that only initial approach can solve.
   As you know arrays in PostgreSQL and other SQL database are not data types for arithmetic operations.
   They are rather data types that help you look up information and form new columns.
   For example, if we want to create table with `unnest` function (which I hope will soon be implemented in Arrow Datafusion)
   ```
   postgres=# SELECT * FROM
     unnest(
       ARRAY[1, 2, 3, 4, 5],
       ARRAY['Ringo', 'George', 'Paul', 'John', NULL],
       ARRAY[29, 27, 27, 29, NULL]
     ) AS data(id,name,age);
    id |  name  | age 
   ----+--------+-----
     1 | Ringo  |  29
     2 | George |  27
     3 | Paul   |  27
     4 | John   |  29
     5 |        |    
   (5 rows)
   ```
   Or find the information:
   ```
   postgres=# SELECT array_positions(array[1, 2, 3, 4, 5], 1);
    array_positions 
   -----------------
    {1}
   (1 row)
   ```
   As I know we can create column with NULLS values.
   So, I think NULLS must exist in their usual understanding (without casting and passes).
   I hope I explained well.
   What do you think?


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