public DataTypePhysicalVariation getDataTypePhysicalVariation(int columnNum) {
      if (scratchDataTypePhysicalVariations == null) {
        return null;
      }
      return scratchDataTypePhysicalVariations[columnNum - initialOutputCol];
    }
Context class for vectorization execution.
Main role is to map column names to column indices and serves as a
factory class for building vectorized expressions out of descriptors.
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/VectorizationContext.java