[jira] [Created] (SPARK-43063) `df.show` handle null should print NULL instead of null

["yikaifei (Jira)" <ji...@apache.org>]

yikaifei created SPARK-43063:
--------------------------------

             Summary: `df.show` handle null should print NULL instead of null
                 Key: SPARK-43063
                 URL: https://issues.apache.org/jira/browse/SPARK-43063
             Project: Spark
          Issue Type: Improvement
          Components: SQL
    Affects Versions: 3.4.0
            Reporter: yikaifei


`df.show` handle null should print NULL instead of null to consistent behavior;

Like as the following behavior is currently inconsistent:
``` shell
scala> spark.sql("select decode(6, 1, 'Southlake', 2, 'San Francisco', 3, 'New Jersey', 4, 'Seattle') as result").show(false)
+------+
|result|
+------+
|null  |
+------+
```
``` shell
spark-sql> DESC FUNCTION EXTENDED decode;
function_desc
Function: decode
Class: org.apache.spark.sql.catalyst.expressions.Decode
Usage:
    decode(bin, charset) - Decodes the first argument using the second argument character set.

    decode(expr, search, result [, search, result ] ... [, default]) - Compares expr
      to each search value in order. If expr is equal to a search value, decode returns
      the corresponding result. If no match is found, then it returns default. If default
      is omitted, it returns null.

Extended Usage:
    Examples:
      > SELECT decode(encode('abc', 'utf-8'), 'utf-8');
       abc
      > SELECT decode(2, 1, 'Southlake', 2, 'San Francisco', 3, 'New Jersey', 4, 'Seattle', 'Non domestic');
       San Francisco
      > SELECT decode(6, 1, 'Southlake', 2, 'San Francisco', 3, 'New Jersey', 4, 'Seattle', 'Non domestic');
       Non domestic
      > SELECT decode(6, 1, 'Southlake', 2, 'San Francisco', 3, 'New Jersey', 4, 'Seattle');
       NULL

    Since: 3.2.0

Time taken: 0.074 seconds, Fetched 4 row(s)
```
``` shell
spark-sql> select decode(6, 1, 'Southlake', 2, 'San Francisco', 3, 'New Jersey', 4, 'Seattle');
NULL
```



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