support final keyword for ClickHouse dialect (#765)

Author: YiuRULE

pypika/dialects.py

@@ -796,9 +796,14 @@ class ClickHouseQueryBuilder(QueryBuilder):
 
     def __init__(self, **kwargs) -> None:
         super().__init__(**kwargs)
+        self._final = False
         self._sample = None
         self._sample_offset = None
 
+    @builder
+    def final(self) -> "ClickHouseQueryBuilder":
+        self._final = True
+
     @builder
     def sample(self, sample: int, offset: Optional[int] = None) -> "ClickHouseQueryBuilder":
         self._sample = sample
@@ -816,6 +821,8 @@ def _from_sql(self, with_namespace: bool = False, **kwargs: Any) -> str:
         if self._delete_from:
             return " {selectable} DELETE".format(selectable=selectable)
         clauses = [selectable]
+        if self._final is not False:
+            clauses.append("FINAL")
         if self._sample is not None:
             clauses.append(f"SAMPLE {self._sample}")
         if self._sample_offset is not None:

pypika/tests/dialects/test_clickhouse.py

@@ -23,6 +23,11 @@ def test_use_SAMPLE_with_offset_keyword(self):
         query = ClickHouseQuery.from_(t).select(t.foo).sample(10, 5)
         self.assertEqual(str(query), 'SELECT "foo" FROM "abc" SAMPLE 10 OFFSET 5')
 
+    def test_use_FINAL_keyword(self):
+        t = Table('abc')
+        query = ClickHouseQuery.from_(t).select(t.foo).final()
+        self.assertEqual(str(query), 'SELECT "foo" FROM "abc" FINAL')
+
 
 class ClickHouseDeleteTests(TestCase):
     table_abc = Table("abc")