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