You can run DDL commands directly on ClickHouse, but after you have a lot of these commands in your codebase, it becomes a pain to manage them. We had these commands defined in a lot of ruby files named <timestamp>_create_table.rb using which we mimicked the way rails and active record manage the app database migrations. Rails and active record also give you a schema.rb which shows the latest state of the app database at all times. After having no schema.rb for a long time, and it becoming a pain to manage the standalone migration files in ruby, we decided to build this to be able to manage migrations for ClickHouse, our analytics database. We love using it and the schema.sql file (with the latest db state) it generates at the end.