Support for DDL expressions etc. about databases

[pvanliefland]

Are you thinking about a solution without SQLAlchemy / Alembic?

[tomchristie]

Kinda. Eg. right now if test cases are using engine.create_all(), engine.drop_all() you're having to use a regular syncronous driver. That's fine but it means that we always have two sets of dependencies. An async database driver for the regular code, and a sync database driver for any migrations or table setup. It'd be nice if we didn't need to do that.

[tomchristie]

Something like...

-    async def execute(self, query: ClauseElement) -> typing.Any:
+    async def execute(
+        self, query: typing.Union[ClauseElement, DDLElement]
+    ) -> typing.Any:
         assert self._connection is not None, "Connection is not acquired"
-        query, args, result_columns = self._compile(query)
-        return await self._connection.fetchval(query, *args)
+        if isinstance(query, DDLElement):
+            compiled = query.compile(dialect=self._dialect).string
+            await self._connection.execute(compiled)
+            return
+        else:
+            query, args, result_columns = self._compile(query)
+            return await self._connection.fetchval(query, *args)