fix: calculate limit value correctly for offset only queries

Author: larkee

google/cloud/sqlalchemy_spanner/sqlalchemy_spanner.py

@@ -260,6 +260,7 @@ def limit_clause(self, select, **kw):
         if select._offset_clause is not None:
             if select._limit_clause is None:
                 text += "\n LIMIT 9223372036854775805"
+                # text += f"\n LIMIT {9223372036854775807-select._offset}"
             text += " OFFSET " + self.process(select._offset_clause, **kw)
         return text
 

test/test_suite.py

@@ -1616,6 +1616,31 @@ def test_staleness(self):
             assert connection.connection.staleness is None
 
 
+class LimitOffsetTest(fixtures.TestBase):
+    """
+    Check that the limit and offset statements are being generated correctly.
+    """
+
+    def setUp(self):
+        self._engine = create_engine(get_db_url(), pool_size=1)
+        self._metadata = MetaData(bind=self._engine)
+
+        self._table = Table(
+            "execution_options",
+            self._metadata,
+            Column("opt_id", Integer, primary_key=True),
+            Column("opt_name", String(16), nullable=False),
+        )
+
+        self._metadata.create_all(self._engine)
+
+    def test_offset_only(self):
+        for offset in [1, 7, 10, 100, 1000, 10000]:
+
+            with self._engine.connect().execution_options(read_only=True) as connection:
+                list(connection.execute(self._table.select().offset(offset)).fetchall())
+
+
 class ComputedReflectionFixtureTest(_ComputedReflectionFixtureTest):
     @classmethod
     def define_tables(cls, metadata):