Use non-subquery form for empty IN

Revised the "EMPTY IN" expression to no longer rely upon using a subquery,
as this was causing some compatibility and performance problems. The new
approach for selected databases takes advantage of using a NULL-returning
IN expression combined with the usual "1 != 1" or "1 = 1" expression
appended by AND or OR. The expression is now the default for all backends
other than SQLite, which still had some compatibility issues regarding
tuple "IN" for older SQLite versions.

Third party dialects can still override how the "empty set" expression
renders by implementing a new compiler method
``def visit_empty_set_op_expr(self, type_, expand_op)``, which takes
precedence over the existing
``def visit_empty_set_expr(self, element_types)`` which remains in place.

Fixes: #6258
Fixes: #6397
Change-Id: I2df09eb00d2ad3b57039ae48128fdf94641b5e59

1 files changed, 5 insertions, 0 deletions

diff --git a/lib/sqlalchemy/dialects/sqlite/base.py b/lib/sqlalchemy/dialects/sqlite/base.py
index 59d40fef0..66a556ae0 100644
--- a/lib/sqlalchemy/dialects/sqlite/base.py
+++ b/lib/sqlalchemy/dialects/sqlite/base.py
@@ -1299,6 +1299,11 @@ class SQLiteCompiler(compiler.SQLCompiler):
             self.process(binary.right, **kw),
         )
 
+    def visit_empty_set_op_expr(self, type_, expand_op):
+        # slightly old SQLite versions don't seem to be able to handle
+        # the empty set impl
+        return self.visit_empty_set_expr(type_)
+
     def visit_empty_set_expr(self, element_types):
         return "SELECT %s FROM (SELECT %s) WHERE 1!=1" % (
             ", ".join("1" for type_ in element_types or [INTEGER()]),