yaooqinn opened a new pull request #27317: [SPARK-30592][SQL] Interval type 
checker for csv and json funtions
URL: https://github.com/apache/spark/pull/27317
 
 
   ### What changes were proposed in this pull request?
   
   In this PR, I'd propose to add interval type checker for the CSV and JSON 
functions, as interval type is going public and we don't want to expose too 
much to the users. 
   
   On one hand, CSV and JSON records consist of string values, in the cast 
logic, we can cast string from/to interval now, so we can make those functions 
support intervals easily.
   BUT on the other hand,  we ban reading (by no suitable converter) or writing 
(with checker) intervals from CSV and JSON files.
   
   Currently, we follow the read/write logic to add type checker for functions. 
   
   As a workaround, you can get a interval from csv or json by expilicit cast, 
e.g.
   ```sql
   SELECT cast(from_csv('1, 1 day', 'a INT, b string').b as interval)
   struct<CAST(from_csv(1, 1 day).b AS INTERVAL):interval>
   1 days
   ```
   
   
   ### Why are the changes needed?
   <!--
   Please clarify why the changes are needed. For instance,
     1. If you propose a new API, clarify the use case for a new API.
     2. If you fix a bug, you can clarify why it is a bug.
   -->
   
   for interval's future-proofing purpose
   
   ### Does this PR introduce any user-facing change?
   <!--
   If yes, please clarify the previous behavior and the change this PR proposes 
- provide the console output, description and/or an example to show the 
behavior difference if possible.
   If no, write 'No'.
   -->
   
   yes, to_json can not use interval type as key you can use legacy config to 
restore.
   ### How was this patch tested?
   <!--
   If tests were added, say they were added here. Please make sure to add some 
test cases that check the changes thoroughly including negative and positive 
cases if possible.
   If it was tested in a way different from regular unit tests, please clarify 
how you tested step by step, ideally copy and paste-able, so that other 
reviewers can test and check, and descendants can verify in the future.
   If tests were not added, please describe why they were not added and/or why 
it was difficult to add.
   -->
   add ut

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