public void setInputContext(String tableName, String partitionName) {
    if (childOperators != null) {
      for (Operator<? extends OperatorDesc> child : childOperators) {
        if (child.getNumParent() == 1) {
          child.setInputContext(tableName, partitionName);
        }
      }
    }
  }
Called during semantic analysis as operators are being added
in order to give them a chance to compute any additional plan information
needed.  Does nothing by default.
ql/src/java/org/apache/hadoop/hive/ql/exec/Operator.java