Proper null handling in LowCardinality columns

mymarilyn · Nov 14, 2019 · 8df7f9a · 8df7f9a
1 parent af87014
commit 8df7f9a
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Showing 2 changed files with 19 additions and 1 deletion.
diff --git a/clickhouse_driver/columns/lowcardinalitycolumn.py b/clickhouse_driver/columns/lowcardinalitycolumn.py
@@ -51,7 +51,7 @@ def _write_data(self, items, buf):
 
         if self.nested_column.nullable:
             # First element represents NULL if column is nullable.
-            index.append(0)
+            index.append(self.nested_column.null_value)
             # Prevent null map writing. Reset nested column nullable flag.
             self.nested_column.nullable = False
 

diff --git a/tests/columns/test_low_cardinality.py b/tests/columns/test_low_cardinality.py
@@ -158,3 +158,21 @@ def test_fixed_string(self):
 
             inserted = self.client.execute(query)
             self.assertEqual(inserted, data)
+
+    @require_server_version(19, 3, 3)
+    def test_nullable_string(self):
+        with self.create_table('a LowCardinality(Nullable(String))'):
+            data = [
+                ('test', ), ('', ), (None, )
+            ]
+            self.client.execute('INSERT INTO test (a) VALUES', data)
+
+            query = 'SELECT * FROM test'
+            inserted = self.emit_cli(query)
+            self.assertEqual(
+                inserted,
+                'test\n\n\\N\n'
+            )
+
+            inserted = self.client.execute(query)
+            self.assertEqual(inserted, data)