public static List<ExprNodeDesc> flattenExprList(List<ExprNodeDesc> sourceList) {
    ArrayList<ExprNodeDesc> result = new ArrayList<ExprNodeDesc>(sourceList.size());
    for (ExprNodeDesc source : sourceList) {
      result.add(flattenExpr(source));
    }
    return result;
  }
Build ExprNodeColumnDesc for the projections in the input operator from
sartpos to endpos(both included). Operator must have an associated
colExprMap.

@param inputOp
         Input Hive Operator
@param startPos
         starting position in the input operator schema; must be &gt;=0 and &lt;=
         endPos
@param endPos
         end position in the input operator schema; must be &gt;=0.
@return List of ExprNodeDesc
ql/src/java/org/apache/hadoop/hive/ql/plan/ExprNodeDescUtils.java