I wasn't clear enough. in Datomic, you upload your entire application code (web server and all) into the database and run it from the same JVM cluster as the database in the same memory space as the database. There is no opportunity for dichotomy between application logic and database logic because the database is serving the application (or the application is serving the database...this is now just a matter of perspective)

Yes, PostgreSQL does this too, you can use JVM/Python/Node etc. But it's not really geared towards being your app server like Datomic is.

Same with MSSQL. You can write stored procedures in C#