[GitHub] [spark] maropu commented on pull request #29983: [SPARK-13860][SQL] Change stddev_samp and var_samp to return 0.0 instead of Double.NaN to align with TPCDS standard.

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

maropu commented on pull request #29983:
URL: https://github.com/apache/spark/pull/29983#issuecomment-706148055


   Really, we need to return 0.0 in the case? Looks PostgreSQL/MySQL returns null instead;
   ```
   mysql> create table t (v float8);
   mysql> insert into t values (1.0);
   mysql> SELECT stddev_samp(v) FROM t;
   +----------------+
   | stddev_samp(v) |
   +----------------+
   |           NULL |
   +----------------+
   1 row in set (0.00 sec)
   
   
   postgres=# create table t (v float8);
   postgres=# insert into t values (1.0);
   INSERT 0 1
   postgres=# \pset null 'null'
   Null display is "null".
   postgres=# SELECT stddev_samp(v) FROM t;
    stddev_samp 
   -------------
           null
   (1 row)
   ```


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