@Override
  public String vectorExpressionParameters() {
    return getColumnParamString(0, inputColumnNum[0]) + ", " + getColumnParamString(1, inputColumnNum[1]) +
        ", " + getColumnParamString(2, inputColumnNum[2]);
  }
Do conditional execution of the THEN/ vector expression and regular execution of the ELSE
vector expression (a column or scalar) of a SQL IF statement.
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/expressions/IfExprCondExprColumn.java