code: protected CharSequence formatSQLValue(String col, Attribute<T, Serializable> attr, final ColumnValue cv) {
          if (cv == null) return null;
          Object val = cv.getValue();
          CryptHandler handler = attr.attach();
          if (handler != null) val = handler.encrypt(val);
          switch (cv.getExpress()) {
              case INC:
                  return new StringBuilder().append(col).append(" + ").append(val);
              case MUL:
                  return new StringBuilder().append(col).append(" * ").append(val);
              case AND:
                  return new StringBuilder().append(col).append(" & ").append(val);
              case ORR:
                  return new StringBuilder().append(col).append(" | ").append(val);
              case MOV:
                  return formatToString(val);
          }
          return formatToString(val);
      }
docs: 拼接UPDATE给字段赋值的SQL片段
  
  @param col  表字段名
  @param attr Attribute
  @param cv   ColumnValue
  
  @return CharSequence