We recently started adding support for CTEs in Vitess! You can check out https://github.com/vitessio/vitess/pull/14321 if you want to see some technical details of the implementation.

For now, we have added preliminary support by converting them to derived tables internally, but we believe that we need to make CTEs first-class citizens themselves of query planning, specifically because recursive CTEs are very hard to model as derived tables. Once we make that change, we can look towards supporting recursive CTEs.

This however will take some time, but then, all good things do!