public String[] getFieldNames(){

        int fieldTypeLength = rowTypeInfo.getFieldTypes().length;
        if( fieldTypeLength == 2
                && rowTypeInfo.getFieldTypes()[1].getClass().equals(BaseRowTypeInfo.class)){
            return ((BaseRowTypeInfo)rowTypeInfo.getFieldTypes()[1]).getFieldNames();
        } else if(fieldTypeLength ==1
                && rowTypeInfo.getFieldTypes()[0].getClass().equals(BaseRowTypeInfo.class)){
            return  ((BaseRowTypeInfo)rowTypeInfo.getFieldTypes()[0]).getFieldNames();
        }else {
            return  rowTypeInfo.getFieldNames();
        }
    }
deal with equation with constant etc. foo.id = 1
@param literal
@param identifier
core/src/main/java/com/dtstack/flink/sql/side/BaseSideInfo.java