unexpected behaviour of dumpling's CollationCompatible

[lance6716]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

use "strict" CollationCompatible in DM

MySQL [sync_collation2]> show create table t2;
+-------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table                                                                                                                                                                                                |
+-------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| t2    | CREATE TABLE `t2` (
  `id` int NOT NULL,
  `name` varchar(20) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1 COLLATE=latin1_bin |
+-------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.000 sec)

$ cat /tmp/dm_test/sync_collation/worker2/dumped_data.sync_collation/sync_collation2.t2-schema.sql 
/*!40101 SET NAMES binary*/;
CREATE TABLE `t2` (`id` INT NOT NULL,`name` VARCHAR(20) CHARACTER SET UTF8MB4 COLLATE utf8mb4_0900_ai_ci COLLATE utf8mb4_general_ci DEFAULT NULL,PRIMARY KEY(`id`)) ENGINE = InnoDB DEFAULT CHARACTER SET = LATIN1 DEFAULT COLLATE = LATIN1_BIN;

note there's two COLLATE

2. What did you expect to see? (Required)

3. What did you see instead (Required)

4. What is your TiDB version? (Required)

[lance6716]

/cc @WizardXiao