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, 46 insertions, 4 deletions

diff --git a/lib/sqlalchemy/sql/compiler.py b/lib/sqlalchemy/sql/compiler.py
index 6168248ff..e9e05b7e9 100644
--- a/lib/sqlalchemy/sql/compiler.py
+++ b/lib/sqlalchemy/sql/compiler.py
@@ -1903,6 +1903,45 @@ class SQLCompiler(Compiled):
             binary, override_operator=operators.match_op
         )
 
+    def visit_in_op_binary(self, binary, operator, **kw):
+        return self._render_in_expr_w_bindparam(binary, operator, **kw)
+
+    def visit_not_in_op_binary(self, binary, operator, **kw):
+        return self._render_in_expr_w_bindparam(binary, operator, **kw)
+
+    def _render_in_expr_w_bindparam(self, binary, operator, **kw):
+        opstring = OPERATORS[operator]
+
+        if isinstance(binary.right, elements.BindParameter):
+            if not binary.right.expanding or not binary.right.expand_op:
+                # note that by cloning here, we rely upon the
+                # _cache_key_bind_match dictionary to resolve
+                # clones of bindparam() objects to the ones that are
+                # present in our cache key.
+                binary.right = binary.right._clone(maintain_key=True)
+                binary.right.expanding = True
+                binary.right.expand_op = operator
+
+        return self._generate_generic_binary(binary, opstring, **kw)
+
+    def visit_empty_set_op_expr(self, type_, expand_op):
+        if expand_op is operators.not_in_op:
+            if len(type_) > 1:
+                return "(%s)) OR (1 = 1" % (
+                    ", ".join("NULL" for element in type_)
+                )
+            else:
+                return "NULL) OR (1 = 1"
+        elif expand_op is operators.in_op:
+            if len(type_) > 1:
+                return "(%s)) AND (1 != 1" % (
+                    ", ".join("NULL" for element in type_)
+                )
+            else:
+                return "NULL) AND (1 != 1"
+        else:
+            return self.visit_empty_set_expr(type_)
+
     def visit_empty_set_expr(self, element_types):
         raise NotImplementedError(
             "Dialect '%s' does not support empty set expression."
@@ -1959,12 +1998,12 @@ class SQLCompiler(Compiled):
             to_update = []
             if parameter.type._is_tuple_type:
 
-                replacement_expression = self.visit_empty_set_expr(
-                    parameter.type.types
+                replacement_expression = self.visit_empty_set_op_expr(
+                    parameter.type.types, parameter.expand_op
                 )
             else:
-                replacement_expression = self.visit_empty_set_expr(
-                    [parameter.type]
+                replacement_expression = self.visit_empty_set_op_expr(
+                    [parameter.type], parameter.expand_op
                 )
 
         elif isinstance(values[0], (tuple, list)):
@@ -3900,6 +3939,9 @@ class StrSQLCompiler(SQLCompiler):
             for t in extra_froms
         )
 
+    def visit_empty_set_op_expr(self, type_, expand_op):
+        return self.visit_empty_set_expr(type_)
+
     def visit_empty_set_expr(self, type_):
         return "SELECT 1 WHERE 1!=1"