Fix the issue where the CHARSET cannot be retrieved in OceanBase.

[davidzhangbj]

• The contributed code is licensed under GPL v2.0
• Contributor Licence Agreement (CLA) is signed
• util/update-modules has been ran
• Documentation updated
• Test suite update

An error occurred while I was using pt-archiver to migrate data from MySQL to OceanBase: "Character set mismatch: --dest DSN uses utf8mb4, table uses . ". It seems that pt-archiver did not correctly detect the character set of the destination database.
I noticed that the format of DDL statements in OceanBase differs slightly from that in MySQL. In MySQL, the output of the SHOW CREATE TABLE command shows the character set without spaces around the equals sign (e.g., CHARSET=utf8mb4). In contrast, OceanBase shows the character set with spaces around the equals sign (e.g., CHARSET = utf8mb4).
To resolve this issue, I modified the regular expression used for matching the character set, and the migration was successful.

mysql DDL statement

mysql> show create table t3;
+-------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+-------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| t3 | CREATE TABLE t3 (
id int(11) NOT NULL AUTO_INCREMENT,
name varchar(20) DEFAULT NULL,
PRIMARY KEY (id)
) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8mb4 |
+-------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

OceanBase DDL statement

obclient [sun_test]> show create table t3;
+-------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+-------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| t3 | CREATE TABLE t3 (
id int(11) NOT NULL AUTO_INCREMENT,
name varchar(20) DEFAULT NULL,
PRIMARY KEY (id)
) AUTO_INCREMENT = 2 DEFAULT CHARSET = utf8mb4 ROW_FORMAT = DYNAMIC |
+-------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.005 sec)

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