add tests for checking precision

data_diff/databases/base.py

@@ -201,6 +201,7 @@ class BaseDialect(abc.ABC):
  SUPPORTS_INDEXES: ClassVar[bool] = False
  PREVENT_OVERFLOW_WHEN_CONCAT: ClassVar[bool] = False
  TYPE_CLASSES: ClassVar[Dict[str, Type[ColType]]] = {}
+ DEFAULT_NUMERIC_PRECISION: ClassVar[int] = 0 # effective precision when type is just "NUMERIC"
 
  PLACEHOLDER_TABLE = None # Used for Oracle
 

data_diff/databases/bigquery.py

@@ -75,6 +75,9 @@ class Dialect(BaseDialect):
  }
  TYPE_ARRAY_RE = re.compile(r"ARRAY<(.+)>")
  TYPE_STRUCT_RE = re.compile(r"STRUCT<(.+)>")
+ # https://cloud.google.com/bigquery/docs/reference/standard-sql/data-types#parameterized_decimal_type
+ # The default scale is 9, which means a number can have up to 9 digits after the decimal point.
+ DEFAULT_NUMERIC_PRECISION = 9
 
  def random(self) -> str:
  return "RAND()"

data_diff/databases/duckdb.py

@@ -45,6 +45,10 @@ class Dialect(BaseDialect):
  SUPPORTS_PRIMARY_KEY = True
  SUPPORTS_INDEXES = True
 
+ # https://duckdb.org/docs/sql/data_types/numeric#fixed-point-decimals
+ # The default WIDTH and SCALE is DECIMAL(18, 3), if none are specified.
+ DEFAULT_NUMERIC_PRECISION = 3
+
  TYPE_CLASSES = {
  # Timestamps
  "TIMESTAMP WITH TIME ZONE": TimestampTZ,

data_diff/databases/postgresql.py

@@ -45,6 +45,12 @@ class PostgresqlDialect(BaseDialect):
  SUPPORTS_PRIMARY_KEY: ClassVar[bool] = True
  SUPPORTS_INDEXES = True
 
+ # https://www.postgresql.org/docs/current/datatype-numeric.html#DATATYPE-NUMERIC-DECIMAL
+ # without any precision or scale creates an “unconstrained numeric” column
+ # in which numeric values of any length can be stored, up to the implementation limits.
+ # https://www.postgresql.org/docs/current/datatype-numeric.html#DATATYPE-NUMERIC-TABLE
+ DEFAULT_NUMERIC_PRECISION = 16383
+
  TYPE_CLASSES: ClassVar[Dict[str, Type[ColType]]] = {
  # Timestamps
  "timestamp with time zone": TimestampTZ,

tests/test_database.py

@@ -134,3 +134,36 @@ def test_three_part_support(self):
  d = db.query_table_schema(part.path)
  assert len(d) == 1
  db.query(part.drop())
+
+
+@test_each_database
+class TestNumericPrecisionParsing(unittest.TestCase):
+ def test_specified_precision(self):
+ name = "tbl_" + random_table_suffix()
+ db = get_conn(self.db_cls)
+ tbl = table(name, schema={"value": "NUMERIC(10, 2)"})
+ db.query(tbl.create())
+ t = table(name)
+ raw_schema = db.query_table_schema(t.path)
+ schema = db._process_table_schema(t.path, raw_schema)
+ self.assertEqual(schema["value"].precision, 2)
+
+ def test_specified_zero_precision(self):
+ name = "tbl_" + random_table_suffix()
+ db = get_conn(self.db_cls)
+ tbl = table(name, schema={"value": "NUMERIC(10)"})
+ db.query(tbl.create())
+ t = table(name)
+ raw_schema = db.query_table_schema(t.path)
+ schema = db._process_table_schema(t.path, raw_schema)
+ self.assertEqual(schema["value"].precision, 0)
+
+ def test_default_precision(self):
+ name = "tbl_" + random_table_suffix()
+ db = get_conn(self.db_cls)
+ tbl = table(name, schema={"value": "NUMERIC"})
+ db.query(tbl.create())
+ t = table(name)
+ raw_schema = db.query_table_schema(t.path)
+ schema = db._process_table_schema(t.path, raw_schema)
+ self.assertEqual(schema["value"].precision, db.dialect.DEFAULT_NUMERIC_PRECISION)