MaxGekk opened a new pull request #27612: [SPARK-30857][SQL][2.4] Fix 
truncations of timestamps before the epoch to minutes and seconds
URL: https://github.com/apache/spark/pull/27612
 
 
   ### What changes were proposed in this pull request?
   In the PR, I propose to replace `%` by `Math.floorMod` in 
`DateTimeUtils.truncTimestamp` for the `HOUR` and `DAY` levels.
   
   ### Why are the changes needed?
   This fixes the issue of incorrect truncation of timestamps before the epoch 
`1970-01-01T00:00:00.000000Z` to the `HOUR` and `DAY` levels. For example, 
timestamps after the epoch are truncated by cutting off the rest part of the 
timestamp:
   ```sql
   spark-sql> select date_trunc('HOUR', '2020-02-11 00:01:02.123'), 
date_trunc('HOUR', '2020-02-11 00:01:02.789');
   2020-02-11 00:00:00  2020-02-11 00:00:00
   ```
   but hours in the truncated timestamp before the epoch are increased by 1:
   ```sql
   spark-sql> select date_trunc('HOUR', '1960-02-11 00:01:02.123'), 
date_trunc('HOUR', '1960-02-11 00:01:02.789');
   1960-02-11 01:00:00  1960-02-11 01:00:00
   ```
   
   ### Does this PR introduce any user-facing change?
   Yes. After the changes, the example above outputs correct result:
   ```sql
   spark-sql> select date_trunc('HOUR', '1960-02-11 00:01:02.123');
   1960-02-11 00:00:00
   ```
   
   ### How was this patch tested?
   Added new tests to `DateFunctionsSuite`.

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