GCP Cloud SQL迁移AWS RDS MySQL时重建索引失败求助

我创建了从AWS RDS MySQL到GCP Cloud SQL实例的持续数据库迁移任务，前期一切正常，但8小时后发现新数据库大小变为0，迁移日志中出现如下错误：

错误信息 #

ERROR: While recreating indexes for table crm.organizations: MySQL Error 1062 (23000): Duplicate entry 'NULL' for key 'organizations.idx_organizations_url'

完整日志条目 #

DUMP_STAGE(RETRY): Attempt 1/2: import failed: loadDump stderr: ERROR: While recreating indexes for table crm.organizations: MySQL Error 1062 (23000): Duplicate entry 'NULL' for key 'organizations.idx_organizations_url': ALTER TABLE crm.organizations ADD FULLTEXT KEY idx_organizations_organizationName_city (organizationName,city),ADD KEY idx_organizations_Company_Id (Company_Id),ADD KEY idx_organizations_state (state),ADD KEY idx_organizations_insertDate (insertDate),ADD KEY idx_organizations_updateDate (updateDate),ADD KEY idx_organizations_organizationName (organizationName),ADD KEY idx_organizations_city (city),ADD KEY idx_organizations_postalCode (postalCode),ADD KEY idx_organizations_industry (industry),ADD KEY idx_organizations_specialty (specialty),ADD KEY idx_organizations_userId (userId),ADD KEY idx_organizations_dateLastActivity (dateLastActivity),ADD KEY idx_organizations_organizationType (organizationType),ADD KEY idx_organizations_phone (phone),ADD KEY idx_organizations_url (url) , ERROR: [Worker000]: While recreating indexes for table crm.organizations: Duplicate entry 'NULL' for key 'organizations.idx_organizations_url'

我无法理解为何会针对url索引报重复条目错误，因为表中确实存在多条url为NULL的记录，且该索引并非唯一索引。

表结构 #

CREATE TABLE `organizations` (
  `organizationId` binary(16) NOT NULL,
  `uuid` varchar(36) GENERATED ALWAYS AS (insert(insert(insert(insert(lower(hex(`organizationId`)),9,0,_utf8mb4'-'),14,0,_utf8mb4'-'),19,0,_utf8mb4'-'),24,0,_utf8mb4'-')) VIRTUAL,
  `Company_Id` bigint DEFAULT NULL,
  `organizationName` varchar(255) DEFAULT NULL,
  `address1` varchar(255) DEFAULT NULL,
  `address2` varchar(255) DEFAULT NULL,
  `city` varchar(60) DEFAULT NULL,
  `state` varchar(60) DEFAULT NULL,
  `postalCode` varchar(20) DEFAULT NULL,
  `country` varchar(60) DEFAULT NULL,
  `latitude` double DEFAULT NULL,
  `longitude` double DEFAULT NULL,
  `url` varchar(255) DEFAULT NULL,
  `phone` varchar(45) DEFAULT NULL,
  `fax` varchar(45) DEFAULT NULL,
  `industry` varchar(45) DEFAULT NULL,
  `specialty` varchar(45) DEFAULT NULL,
  `notes` longtext,
  `userId` binary(16) DEFAULT NULL,
  `userUuid` varchar(36) GENERATED ALWAYS AS (insert(insert(insert(insert(lower(hex(`userId`)),9,0,_utf8mb4'-'),14,0,_utf8mb4'-'),19,0,_utf8mb4'-'),24,0,_utf8mb4'-')) VIRTUAL,
  `organizationType` varchar(255) DEFAULT NULL COMMENT 'organizationType',
  `dateLastActivity` datetime DEFAULT NULL,
  `insertDate` datetime DEFAULT CURRENT_TIMESTAMP,
  `updateDate` datetime DEFAULT NULL ON UPDATE CURRENT_TIMESTAMP,
  PRIMARY KEY (`organizationId`),
  KEY `idx_organizations_Company_Id` (`Company_Id`),
  KEY `idx_organizations_state` (`state`),
  KEY `idx_organizations_insertDate` (`insertDate`),
  KEY `idx_organizations_updateDate` (`updateDate`),
  KEY `idx_organizations_organizationName` (`organizationName`),
  KEY `idx_organizations_city` (`city`),
  KEY `idx_organizations_postalCode` (`postalCode`),
  KEY `idx_organizations_industry` (`industry`),
  KEY `idx_organizations_specialty` (`specialty`),
  KEY `idx_organizations_userId` (`userId`),
  KEY `idx_organizations_dateLastActivity` (`dateLastActivity`),
  KEY `idx_organizations_organizationType` (`organizationType`),
  KEY `idx_organizations_phone` (`phone`),
  KEY `idx_organizations_url` (`url`),
  FULLTEXT KEY `idx_organizations_organizationName_city` (`organizationName`,`city`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci;

我尝试通过导出源表并导入到本地无索引数据库，再用单条ALTER TABLE语句添加索引的方式复现问题，但未成功。

环境信息：AWS RDS MySQL版本为8.0.34，Cloud SQL MySQL版本为8.0.31，我认为这并非报错原因。

恳请提供排查思路。

内容的提问来源于stack exchange，提问作者Ian Herbert