[GitHub] [spark] maropu commented on pull request #29152: [SPARK-32356][SQL] Forbid create view with null type

[GitBox <gi...@apache.org>]

maropu commented on pull request #29152:
URL: https://github.com/apache/spark/pull/29152#issuecomment-661902376


   hm, at least, most databases can accpet it `create view v as select null`, but `null` is regared as another type, e.g., a text in postgresql;
   ```
   postgres=# create view v as select null;
   CREATE VIEW
   postgres=# \d v
                    View "public.v"
     Column  | Type | Collation | Nullable | Default 
   ----------+------+-----------+----------+---------
    ?column? | text |           |          | 
   ```
   MySQL: http://sqlfiddle.com/#!9/42febe/1/0
   SQLite: http://sqlfiddle.com/#!7/42feb/1/0
   
   So, IMO accepting it looks somewhat meaningful to follow other databases, but we don't need to handle it as a null type. Either way, I think its better to update the migration guide if we change thsi behaivour.


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