Tian Jiang created IOTDB-514:
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             Summary: To support aggregation in the distributed version
                 Key: IOTDB-514
                 URL: https://issues.apache.org/jira/browse/IOTDB-514
             Project: Apache IoTDB
          Issue Type: Improvement
            Reporter: Tian Jiang
             Fix For: master branch


The current aggregation cannot satisfy the needs in the distributed version, to 
be specific, there are two points that should be satisfied:
1. The FirstValueAggrResult and LastValueAggrResult should also contain 
timestamp.
Without a timestamp, the coordinator node cannot tell the result from which 
node is the true first/last.
2. An AggrResult should be able to merge with another. When we get AggrResults 
from all nodes that participate in the query, these results should be merged to 
generate a new result.

To resolve the issue, you should:
1. Add a field `timestamp` in FirstValueAggrResult and LastValueAggrResult
2. Add an abstract method `merge(AggregateResult another)` in AggregateResult 
and implement it properly.



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