`SHOW FULL COLUMNS` fail to show a table/column comments

[tshqin]

1. What did you do?

I exported mysql DDL-s by using mysqldump with parameter --no-data, so I got DDL-s like below:

CREATE TABLE `t_bs_s_data_item` (
  `ITEM_CD` varchar(10) NOT NULL COMMENT '数据项代码  ',
  `ITEM_NM` varchar(50) NOT NULL COMMENT '数据项名称',
  `ITEM_TYPE` varchar(20) NOT NULL COMMENT '数据项值类型',
  `TS` timestamp NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP COMMENT '时间戳',
  `NT` varchar(256) DEFAULT NULL COMMENT '备注'
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COMMENT='数据项表';

I got success msgs after executed all the DDL-s in TiDB, but all the table/column comments seem missing.

2. What did you expect to see?

MySQL > SHOW FULL COLUMNS FROM t_bs_s_data_item;
+-----------+--------------+-----------------+------+-----+-------------------+-----------------------------+---------------------------------+--------------------+
| Field     | Type         | Collation       | Null | Key | Default           | Extra                       | Privileges                      | Comment            |
+-----------+--------------+-----------------+------+-----+-------------------+-----------------------------+---------------------------------+--------------------+
| ITEM_CD   | varchar(10)  | utf8_general_ci | NO   |     | NULL              |                             | select,insert,update,references | 数据项代码         |
| ITEM_NM   | varchar(50)  | utf8_general_ci | NO   |     | NULL              |                             | select,insert,update,references | 数据项名称         |
| ITEM_TYPE | varchar(20)  | utf8_general_ci | NO   |     | NULL              |                             | select,insert,update,references | 数据项值类型       |
| TS        | timestamp    | NULL            | YES  |     | CURRENT_TIMESTAMP | on update CURRENT_TIMESTAMP | select,insert,update,references | 时间戳             |
| NT        | varchar(256) | utf8_general_ci | YES  |     | NULL              |                             | select,insert,update,references | 备注               |
+-----------+--------------+-----------------+------+-----+-------------------+-----------------------------+---------------------------------+--------------------+
5 rows in set (0.00 sec)

3. What did you see instead?

comments are missing:

TiDB > SHOW FULL COLUMNS FROM t_bs_s_data_item;
+-----------+--------------+-----------+------+------+-------------------+-----------------------------+---------------------------------+---------+
| Field     | Type         | Collation | Null | Key  | Default           | Extra                       | Privileges                      | Comment |
+-----------+--------------+-----------+------+------+-------------------+-----------------------------+---------------------------------+---------+
| ITEM_CD   | varchar(10)  | utf8_bin  | NO   |      | NULL              |                             | select,insert,update,references |         |
| ITEM_NM   | varchar(50)  | utf8_bin  | NO   |      | NULL              |                             | select,insert,update,references |         |
| ITEM_TYPE | varchar(20)  | utf8_bin  | NO   |      | NULL              |                             | select,insert,update,references |         |
| TS        | timestamp    | binary    | YES  |      | CURRENT_TIMESTAMP | on update CURRENT_TIMESTAMP | select,insert,update,references |         |
| NT        | varchar(256) | utf8_bin  | YES  |      | NULL              |                             | select,insert,update,references |         |
+-----------+--------------+-----------+------+------+-------------------+-----------------------------+---------------------------------+---------+
5 rows in set (0.00 sec)

4. What version of TiDB are you using (tidb-server -V)?

[tidb@TiDB_PD bin]$ ./tidb-server -V
Git Commit Hash: 365e4ab491b683a69c2004f30b1ae4f86256e2ad
Git Commit Branch: master
UTC Build Time:  2017-08-16 01:24:27

[tshqin]

some additional info:
MySQL [gin]> SELECT COLUMN_COMMENT FROM INFORMATION_SCHEMA.COLUMNS where table_name='t_bs_s_data_item';
+----------------+
| COLUMN_COMMENT |
+----------------+
| |
| |
| |
| |
| |
| |
| |
| |
| |
| |
+----------------+
10 rows in set (0.03 sec)

MySQL [gin]> SELECT * FROM INFORMATION_SCHEMA.COLUMNS where trim(COLUMN_COMMENT)<>'';
Empty set (0.01 sec)