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Yes, moving from a completely different database system, requires quite a bit of knowledge about SQL to pull off and will be a lot of manual labor.

You can find a full documentation about the history of all (mysql) tables via Manual:Database layout. You will probably want to peruse through all that in order to make it work. I would definitely setup a mysql 1.27 with a mysql setup first to do the SQL to MySQL data migration, before getting started on the actual data migration.

There is also the history of the entire mssql schema at https://gerrit.wikimedia.org/r/plugins/gitiles/mediawiki/core/+/refs/heads/REL1_33/maintenance/mssql/

However note that already in 1.33 mssql had major broken parts and was lagging behind the other schema changes, so I would not use it to upgrade to the 1.33 schema. It and it's history may however help in figuring out the history of the schema.