public static ColumnInfo resolveColumn(RowSchema rs,
      ExprNodeColumnDesc desc) {
    ColumnInfo ci = rs.getColumnInfo(desc.getTabAlias(), desc.getColumn());
    if (ci == null) {
      ci = rs.getColumnInfo(desc.getColumn());
    }
    if (ci == null) {
      return null;
    }
    return ci;
  }
Get ColumnInfo from column expression.

@param rs
@param desc
@return
ql/src/java/org/apache/hadoop/hive/ql/optimizer/ConstantPropagateProcFactory.java