If bigquery is installed, the unnest function (defined here) overrides the unnest function for all dialects.

In PostgreSQL usage of unnest is allowed with column identifiers (unnesting an array contained in a table column). But the global re-definition of unnest caused by bigquery makes code like this sa.func.unnest(some_column) fail with TypeError: The argument to unnest must have an ARRAY type. because, obviously, a column is not an array literal.

In my case I really do need many dialects installed at the same time.