Github user adrian-wang commented on the pull request:
https://github.com/apache/spark/pull/7589#issuecomment-123745566
@rxin On my second thought, I think we should keep date_add and date_sub as
simple as it should be. When it comes to Datetime IntervalType computation, we
need another node specially for this. Here are my considerations:
1. hive 1.2 supports interval type, but still keep date_add and date_sub
simple.
2, use another node can keep the registered function the same as most
database systems.
3. for strings, it is hard to decide whether it is a date or timestamp,
this would be troublesome. For most databases, we use `date '2015-01-01' +
interval XXXX` to do this calculation. so the sql engine could know how we
should take care of the string here.
And I have several other TODOS for the simple POC shown here, as follows:
1. we need to let us be aware of the precision of the interval type. For
the calculation here, we would return DateType if we are add a Date and an
Year-Month Interval, otherwise we should return TimestampType. For POC shown
here, I just use TimestampType as the general returning type. Maybe we need two
interval types here.
2. I need to get add support in parser. to translate the `shiptime +
interval XXXX` into corresponding logical node.
2-1. the left operand of `timestamp '2015-01-01 11:22:33' + interval XXXX`
should be translated into a Cast that cast string into corresponding type.
2-2. Then we translate the calculation to a TimeAdd or a TimeSub.
I think the whole stuff deserves another PR.
cc @chenghao-intel
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