[GitHub] [arrow-datafusion] jackwener commented on pull request #3771: Teach a negative NULL expression to return NULL instead of an error

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

jackwener commented on PR #3771:
URL: https://github.com/apache/arrow-datafusion/pull/3771#issuecomment-1272499097

   PG will deduce the type of null based on other parameters.
   
   we can specify the null type, it will ok.
   ```sql
   jackwener=# select -null::int;
    ?column?
   ----------
   
   (1 row)
   ```
   
   deduce the type of null based on other parameters.
   ```sql
   jackwener=# select 1+null;
    ?column?
   ----------
   
   (1 row)
   ```
   
   error, can't deduce
   ```sql
   =# select null+null;
   ERROR:  operator is not unique: unknown + unknown
   LINE 1: select null+null;
                      ^
   HINT:  Could not choose a best candidate operator. You might need to add explicit type casts.
   leiysky=#
   ```
   


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