For any database migration we should follow below practices.
1. Evaluate Complexity of Data
2. Establish Data Standards
3. Define Current and Future Business Rules
4. Establish Information Governance Roles and
Responsibilities
5. Perform Data Quality Assessment
6. Gather Migration Requirements
7. Assess and Identify the Proper Tool
8. Risk Management
9. Organizational
Changes
10. Migration Testing
Some Different Database
Migration Link : -
Migrate Oracle Database to PostgreSQL
SQL Server database migration best practices for low risk and
downtime
https://www.sqlshack.com/sql-server-database-migration-best-practices-low-risk-downtime/
Data Migration Best Practices
Migrate Oracle Database to MySql
https://www.xaprb.com/blog/2009/03/13/50-things-to-know-before-migrating-oracle-to-mysql/
Migrate PostgreSQL to MySQL using the MySQL Workbench Migration
Wizard
MySQL
to PostgreSQL Migration