huaxingao commented on pull request #29043:
URL: https://github.com/apache/spark/pull/29043#issuecomment-657179299
@TJX2014
I am still not convinced that it's a good idea to map TimeStamp to DateTime
in MySQLDialect. Using an example similar to yours:
```
sql("select cast('1970-01-01 00:00:01' as
timestamp)").toDF("ts").write.mode("append").jdbc("jdbc:mysql://localhost:3306/test",
"ts_test3",prop)
```
Since user explicitly cast string to timestamp, I would think that the user
wants to insert 1970-01-0 00:00:01 as a TimeStamp data type. Suppose the
current time zone on mysql server is america/los_angeles. After the data is
inserted to mysql, if the user changes the time zone setting
SET TIME_ZONE = "america/new_york";
Then the user would expect to get 1970-01-01 03:00:01 when retrieving the
timestamp. But with this patch, we silently change the data type from TimeStamp
to DateTime, after user insert the timestamp and change the time zone setting,
user will still get 1970-01-0 00:00:01 which is not the correct value.
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