Are MySQL 8 Features like CTE Supported?

[jdevries3133]

Common table expressions were introduce to MySQL in v8. Knex has some issues with MySQL 8 stemming from the MySQL 8 driver not being supported by mysqljs, which I assume that knex depends on; see mysqljs/mysql#1959.

Regardless of this underlying driver incompatibility, it seems that CTE expressions crafted with the .with method of knex's query builder are working against MySQL in practice.

The knex docs, however, document that this usage is not supported:

"With" clauses are supported by PostgreSQL, Oracle, SQLite3 and MSSQL

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Is this compatibility in practice accidental? Is it tested? Should it be documented to work? Should the .with method throw an exception or emit a warning if used with MySQL because the use case is unsupported?

Thanks!