fix(trino): treat DECIMAL(p) as scale 0, not a default non-zero scale (#2404)

core/wren/src/wren/connector/trino.py

@@ -101,7 +101,12 @@ def _trino_data_type_to_arrow(node) -> pa.DataType:
         return _TRINO_DATA_TYPE_TO_ARROW[kind]
 
     if kind == T.DECIMAL:
-        precision, scale = 38, 9
+        # Trino DECIMAL semantics: DECIMAL(p) is precision p with scale 0, and
+        # bare DECIMAL is DECIMAL(38, 0). Defaulting the scale to a non-zero
+        # value mistyped precision-only DECIMAL columns and, for small
+        # precisions (e.g. DECIMAL(5)), produced scale > precision, which
+        # PyArrow rejects with an ArrowInvalid.
+        precision, scale = 38, 0
         params = node.expressions
         if len(params) >= 1:
             with contextlib.suppress(AttributeError, ValueError):

core/wren/tests/connectors/test_trino.py

@@ -64,7 +64,10 @@ _SCHEMA = "default"
         # Decimal
         ("decimal(10,2)", pa.decimal128(10, 2)),
         ("decimal(38,9)", pa.decimal128(38, 9)),
-        ("decimal", pa.decimal128(38, 9)),
+        # DECIMAL(p) is scale 0 and bare DECIMAL is DECIMAL(38, 0) in Trino.
+        ("decimal", pa.decimal128(38, 0)),
+        ("decimal(10)", pa.decimal128(10, 0)),
+        ("decimal(5)", pa.decimal128(5, 0)),
         # Time / timestamp
         ("time", pa.time64("us")),
         ("time(3)", pa.time64("us")),

core/wren/tests/unit/test_athena_connector.py

@@ -74,8 +74,20 @@ def test_parse_athena_type_primitives(type_str, expected):
     assert _parse_athena_type(type_str) == expected
 
 
-def test_parse_athena_type_decimal():
-    assert _parse_athena_type("decimal(12,4)") == pa.decimal128(12, 4)
+@pytest.mark.parametrize(
+    ("type_str", "expected"),
+    [
+        ("decimal(12,4)", pa.decimal128(12, 4)),
+        # bare DECIMAL and precision-only DECIMAL(p) default to scale 0
+        # (kept aligned with the Trino parser).
+        ("decimal", pa.decimal128(38, 0)),
+        ("decimal(10)", pa.decimal128(10, 0)),
+        # small precision must not produce scale > precision (ArrowInvalid).
+        ("decimal(5)", pa.decimal128(5, 0)),
+    ],
+)
+def test_parse_athena_type_decimal(type_str, expected):
+    assert _parse_athena_type(type_str) == expected
 
 
 def test_parse_athena_type_decimal_precision_only_is_scale_zero():
@@ -94,6 +106,21 @@ def test_parse_athena_type_decimal_small_precision_only():
     assert _parse_athena_type("decimal(5)") == pa.decimal128(5, 0)
 
 
+def test_parse_athena_type_decimal_bare_defaults_to_scale_0():
+    # Bare DECIMAL is DECIMAL(38, 0) in Athena/Trino semantics.
+    assert _parse_athena_type("decimal") == pa.decimal128(38, 0)
+
+
+def test_parse_athena_type_decimal_precision_only_has_scale_0():
+    # DECIMAL(p) is precision p with scale 0, not a default non-zero scale.
+    assert _parse_athena_type("decimal(10)") == pa.decimal128(10, 0)
+
+
+def test_parse_athena_type_decimal_small_precision_only():
+    # Small precision-only case must not produce scale > precision (ArrowInvalid).
+    assert _parse_athena_type("decimal(5)") == pa.decimal128(5, 0)
+
+
 def test_parse_athena_type_array():
     assert _parse_athena_type("array(varchar)") == pa.list_(pa.string())