feat: Enhance IN/NOT IN operator handling for empty lists

Added logic to return appropriate criteria for empty lists in IN and NOT IN operators. An empty list with IN now returns 0 results (1=0), while NOT IN returns all results (1=1). Updated tests to verify this behavior.

frappe/database/query.py

@@ -579,6 +579,20 @@ class Engine:
 					v.strip().strip("'") for v in get_between_date_filter(_value, df).split(" AND ")
 				)
 
+		# Handle empty lists for IN/NOT IN operators before conversion
+		# IN with empty list should return 0 results (always False)
+		# NOT IN with empty list should return all results (always True)
+		if _operator.lower() in ("in", "not in"):
+			if isinstance(_value, (list, tuple, set)) and len(_value) == 0:
+				if _operator.lower() == "in":
+					# Return a criterion that always evaluates to False (1=0)
+					# This ensures IN with empty list returns 0 results
+					return RawCriterion("1=0")
+				else:  # not in
+					# Return a criterion that always evaluates to True (1=1)
+					# NOT IN with empty set matches all rows since nothing is excluded
+					return RawCriterion("1=1")
+
 		if not _value and isinstance(_value, list | tuple | set):
 			_value = ("",)
 

frappe/model/db_query.py

@@ -868,6 +868,15 @@ from {tables}
 			if f.operator.lower() == "in":
 				can_be_null &= not f.value or any(v is None or v == "" for v in f.value)
 
+			# Handle empty lists for IN/NOT IN operators before processing
+			# IN with empty list should return 0 results (always False: 1=0)
+			# NOT IN with empty list should return all results (always True: 1=1)
+			if isinstance(f.value, (list, tuple)) and len(f.value) == 0:
+				if f.operator.lower() == "in":
+					return "1=0"
+				else:  # not in
+					return "1=1"
+
 			if value is None:
 				values = f.value or ""
 				if isinstance(values, str):

frappe/tests/test_query.py

@@ -410,12 +410,22 @@ class TestQuery(IntegrationTestCase):
 			"SELECT `name` FROM `tabDocType` WHERE `name` IN ('ToDo','Note')",
 		)
 
+		# Empty list with IN operator should return 0 results (1=0 condition)
 		self.assertQueryEqual(
 			frappe.qb.get_query(
 				"DocType",
 				filters={"name": ("in", [])},
 			).get_sql(),
-			"SELECT `name` FROM `tabDocType` WHERE `name` IN ('')",
+			"SELECT `name` FROM `tabDocType` WHERE 1=0",
+		)
+
+		# Empty list with NOT IN operator should return all results (1=1 condition)
+		self.assertQueryEqual(
+			frappe.qb.get_query(
+				"DocType",
+				filters={"name": ("not in", [])},
+			).get_sql(),
+			"SELECT `name` FROM `tabDocType` WHERE 1=1",
 		)
 
 		self.assertQueryEqual(