fix(clickhouse): fix listing tables from databases with no tables

Author: cpcloud

ibis/backends/clickhouse/__init__.py

@@ -109,11 +109,16 @@ def current_database(self):
 
     def list_databases(self, like=None):
         data, _ = self.raw_sql('SELECT name FROM system.databases')
+        # in theory this should never be empty
+        if not data:  # pragma: no cover
+            return []
         databases = list(data[0])
         return self._filter_with_like(databases, like)
 
     def list_tables(self, like=None, database=None):
         data, _ = self.raw_sql('SHOW TABLES')
+        if not data:
+            return []
         databases = list(data[0])
         return self._filter_with_like(databases, like)
 

ibis/backends/clickhouse/tests/test_client.py

@@ -173,3 +173,15 @@ def test_insert_with_more_columns(temporary_alltypes, df):
 def test_get_schema_using_query(con, query, expected_schema):
     result = con._get_schema_using_query(query)
     assert result == expected_schema
+
+
+def test_list_tables_empty(con, worker_id):
+    dbname = f"tmpdb_{worker_id}"
+    db = con.current_database
+    con.raw_sql(f"CREATE DATABASE IF NOT EXISTS {dbname}")
+    try:
+        con.raw_sql(f"USE {dbname}")
+        assert not con.list_tables()
+    finally:
+        con.raw_sql(f"USE {db}")
+        con.raw_sql(f"DROP DATABASE IF EXISTS {dbname}")