Fix BUG: read_sql tries to convert blob/varbinary to string with pyarrow backend

doc/source/whatsnew/v2.3.0.rst

@@ -130,7 +130,7 @@ MultiIndex
 
 I/O
 ^^^
--
+- Bug in :func:`read_sql` causing an unintended exception when byte data was being converted to string when using the pyarrow dtype_backend (:issue:`59242`)
 -
 
 Period

pandas/core/internals/construction.py

@@ -970,7 +970,17 @@ def convert(arr):
                     if dtype_backend != "numpy" and arr.dtype == np.dtype("O"):
                         new_dtype = StringDtype()
                         arr_cls = new_dtype.construct_array_type()
-                        arr = arr_cls._from_sequence(arr, dtype=new_dtype)
+                        try:
+                            # Addressing (#59242)
+                            # Byte data that could not be decoded into
+                            # a string would throw a UnicodeDecodeError exception
+
+                            # Try and greedily convert to string
+                            # Will fail if the object is bytes
+                            arr = arr_cls._from_sequence(arr, dtype=new_dtype)
+                        except UnicodeDecodeError:
+                            pass
+
                 elif dtype_backend != "numpy" and isinstance(arr, np.ndarray):
                     if arr.dtype.kind in "iufb":
                         arr = pd_array(arr, copy=False)

pandas/tests/io/test_sql.py

@@ -4352,3 +4352,18 @@ def test_xsqlite_if_exists(sqlite_buildin):
         (5, "E"),
     ]
     drop_table(table_name, sqlite_buildin)
+
+
+def test_bytes_column(sqlite_buildin):
+    pytest.importorskip("pyarrow")
+    """
+    Regression test for (#59242)
+    Bytes being returned in a column that could not be converted
+    to a string would raise a UnicodeDecodeError
+    when using dtype_backend='pyarrow'
+    """
+    query = """
+    select cast(x'0123456789abcdef0123456789abcdef' as blob) a
+    """
+    df = pd.read_sql(query, sqlite_buildin, dtype_backend="pyarrow")
+    assert df.a.values[0] == b"\x01#Eg\x89\xab\xcd\xef\x01#Eg\x89\xab\xcd\xef"