Merge pull request #11861 from grahamjeffries/bugfix-11522

BUG: force list type for tuples from chunked sql table reads #11522

doc/source/whatsnew/v0.18.0.txt

@@ -245,3 +245,4 @@ Bug Fixes
 - Bug in ``Index`` prevents copying name of passed ``Index``, when a new name is not provided (:issue:`11193`)
 
 - Bug in ``read_excel`` failing to read any non-empty sheets when empty sheets exist and ``sheetname=None`` (:issue:`11711`)
+- Bug in ``read_sql`` with pymysql connections failing to return chunked data (:issue:`11522`)

pandas/io/sql.py

@@ -1556,6 +1556,8 @@ def _query_iterator(cursor, chunksize, columns, index_col=None,
 
         while True:
             data = cursor.fetchmany(chunksize)
+            if type(data) == tuple:
+               data = list(data)
             if not data:
                 cursor.close()
                 break

pandas/io/tests/test_sql.py

@@ -2477,6 +2477,21 @@ def test_write_row_by_row(self):
         result.index = frame.index
         tm.assert_frame_equal(result, frame)
 
+    def test_chunksize_read_type(self):
+        _skip_if_no_pymysql()
+        frame = tm.makeTimeDataFrame()
+        frame.index.name = "index"
+        drop_sql = "DROP TABLE IF EXISTS test"
+        cur = self.conn.cursor()
+        cur.execute(drop_sql)
+        sql.to_sql(frame, name='test', con=self.conn, flavor='mysql')
+        query = "select * from test"
+        chunksize = 5
+        chunk_gen = pd.read_sql_query(sql=query, con=self.conn,
+                                      chunksize=chunksize, index_col="index")
+        chunk_df = next(chunk_gen)
+        tm.assert_frame_equal(frame[:chunksize], chunk_df)
+
     def test_execute(self):
         _skip_if_no_pymysql()
         frame = tm.makeTimeDataFrame()