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Mike Bayer
ef7ff058eb
As part of the SQLAlchemy 2.0 migration project, a conceptual change has been made to the role of the :class:`.SelectBase` class hierarchy, which is the root of all "SELECT" statement constructs, in that they no longer serve directly as FROM clauses, that is, they no longer subclass :class:`.FromClause`. For end users, the change mostly means that any placement of a :func:`.select` construct in the FROM clause of another :func:`.select` requires first that it be wrapped in a subquery first, which historically is through the use of the :meth:`.SelectBase.alias` method, and is now also available through the use of :meth:`.SelectBase.subquery`. This was usually a requirement in any case since several databases don't accept unnamed SELECT subqueries in their FROM clause in any case. See the documentation in this change for lots more detail. Fixes: #4617 Change-Id: I0f6174ee24b9a1a4529168e52e855e12abd60667