I modified the spark.version in pom.xml,using spark1.6.2, then compliation
There was a "unused import statement" warinng in CarbonOptimizer class before,
we imported AggregationExpression like the following :
But in spark1.6.2, AggregateExpressions is moved to subpackage "aggregate" from
"expressions"(that is for spark1.5.2).
So if we didn't known this change, we removed this import "import
org.apache.spark.sql.catalyst.expressions.aggregate._", it will cause
compliation failure when using spark1.6.2
So, maybe the CI should verify carbondata based on different version spark,
then it will be more helful to check the correctness of the commits, shall we?