Steps to migrate a MySQL database to PostgreSQL?

PostgreSQL vs. MySQL is an important decision when it comes to choosing an open-source relational database management system. Both PostgreSQL and MySQL are time-proven solutions

PostgreSQL is The world’s most advanced open source database, and MySql is popular for ease of development.

First thing WHY your project need to switch the database, consider below before you decide. 

Is current DB using any store procs, functions, triggers, TEMP tables TINYINT(1), Unsigned integer, HASH, KEY, scheduled events etc.

Once you decided to migrate existing MySql to PostgresQL then Export data from MySQL using tools like pgLoader or custom scripts. Modify the SQL dump to match the PostgreSQL syntax. You need to adjust data types, column lengths, and function, procedure calls to take advantage of pgSQL features. watch out for triggers / task scheduler etc.

Use the migration tool to transfer the data from the MySQL database to the PostgreSQL database.

Once data is migrated without any errors then you need to change your apps libraries , db connections, modify SQL queries in app code(Need to change syntax for some queries probably not all queries.)

DO Rigorous testing. Once you are confident then try adding and use advance feature of PostgreSQL LIKE FULL OUTER JOIN, Full-text search, CASCADE option to drop table’s dependent objects e.g., tables and views, Analytic functions, Data types array, hstore, and user-defined type, Boolean type, IP address data type, CHECK constraint, Partial indexes, Bitmap indexes etc.

DB optimization is endless process, you can add features step by step, Rigorous testing is essential for every step. 

IMPORTANT : USE BACKUP AND RECOVERY FEATURES FOR EVERY STEP YOU PERFORM SO THAT YOU CAN COME BACK TO STABLE STATE IF SOMETHING WENT WRONG.