yaooqinn opened a new pull request #28706:
URL: https://github.com/apache/spark/pull/28706
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### What changes were proposed in this pull request?
This PR disables week-based date filed for parsing
### Why are the changes needed?
1. It's an un-fixable behavior change to fill the gap between
SimpleDateFormat and DateTimeFormater and backward-compatibility for different
JDKs.A lot of effort has been made to prove it at
https://github.com/apache/spark/pull/28674
2. The existing behavior itself in 2.4 is confusing, e.g.
```sql
spark-sql> select to_timestamp('1', 'w');
1969-12-28 00:00:00
spark-sql> select to_timestamp('1', 'u');
1970-01-05 00:00:00
```
The 'u' here seems not to go to the Monday of the first week in week-based
form or the first day of the year in non-week-based form but go to the Monday
of the second week in week-based form.
```sql
spark-sql> select to_timestamp('2020 2020', 'YYYY yyyy');
2020-01-01 00:00:00
spark-sql> select to_timestamp('2020 2020', 'yyyy YYYY');
2019-12-29 00:00:00
spark-sql> select to_timestamp('2020 2020 1', 'YYYY yyyy w');
NULL
spark-sql> select to_timestamp('2020 2020 1', 'yyyy YYYY w');
2019-12-29 00:00:00
```
I think we don't need to introduce all the weird behavior from Java
3. The current test coverage for week-based date fields is almost 0%, which
indicates that we've never imagined using it.
4. Avoiding JDK bugs
https://issues.apache.org/jira/browse/SPARK-31880
### Does this PR introduce _any_ user-facing change?
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Yes, the 'Y/W/w/u/F/E' pattern cannot be used datetime parsing functions.
### How was this patch tested?
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more tests added
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