@Override
  public String vectorExpressionParameters() {
    return getColumnParamString(0, inputColumnNum[0]) + ", " + getColumnParamString(1, inputColumnNum[1]);
  }
This class performs OR expression on two input columns and stores,
the boolean output in a separate output column. The boolean values
are supposed to be represented as 0/1 in a long vector.
The first input column field is reused from VectorExpression.
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/expressions/ColOrCol.java