Github user gatorsmile commented on the issue:
https://github.com/apache/spark/pull/16422
To get the column names and types, we do not need `DESC COLUMN`.
For retrieving the statistics, each vendor has different ways. Normally,
users can access the statistics from the catalog tables/views or data
dictionary views. AFAIK, I do not know any system offers `DESC COLUMN`, except
the Hive-like system. [Hive 2.x also has a different syntax from Hive
1.x](https://cwiki.apache.org/confluence/display/Hive/LanguageManual+DDL#LanguageManualDDL-Hive2.0+:SyntaxChange).
In this PR, we follow Hive 2.x.
The complex types can be achieved in RDBMS by UDT. For example, in Oracle,
the logical mapping of structured type is abstract data types. Also, DB2
documents how to use the structured type in the
[link](http://www.ibm.com/support/knowledgecenter/SSEPGG_11.1.0/com.ibm.db2.luw.admin.structypes.doc/doc/t0006603.html).
To access the nested field, it is using double dots (e.g., `col1..field1`). :
)
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