code: public static String tableName(String fieldFullyQualifiedName) {
          if (fieldFullyQualifiedName.contains(".")) {
              return fieldFullyQualifiedName.substring(0, fieldFullyQualifiedName.indexOf("."));
          }
          return null;
      }
docs: 从完全标识字段名获取表名
  
  @param fieldFullyQualifiedName fieldFullyQualifiedName
  @return tableName