Implement date_trunc() function

[alamb]

Note: migrated from original JIRA: https://issues.apache.org/jira/browse/ARROW-12391

Implement the date_trunc function, as described in this PostGres manual:

[https://www.postgresql.org/docs/current/functions-datetime.html#FUNCTIONS-DATETIME-TRUNC]

 

This would allow for the following use cases to be solved:

• casting of timestamps to other resolutions, such as millis and micros
• rounding dates/timestamps 

It also allows the user to explicitly allow the truncation of timestamp precision.

[jwdeitch]

Looks like this was implemented in e5d1471

datafusion/src/physical_plan/datetime_expressions.rs:311

:)

[jorgecarleitao]

Agreed :)

[alamb]

Thanks @jwdeitch !