Using the Snowflake SQLAlchemy toolkit with the Python Connector

Snowflake SQLAlchemy runs on the top of the Snowflake Connector for Python as a dialect to bridge a Snowflake database and SQLAlchemy applications.

For more information, see the dialect documentation.

Prerequisites

Snowflake Connector for Python

The only requirement for Snowflake SQLAlchemy is the Snowflake Connector for Python; however, the connector does not need to be installed because installing Snowflake SQLAlchemy automatically installs the connector.

Data analytics and web application frameworks (optional)

Snowflake SQLAlchemy can be used with pandas, Jupyter, and Pyramid, which provide higher levels of application frameworks for data analytics and web applications. However, building a working environment from scratch is not a trivial task, particularly for novice users. Installing the frameworks requires C compilers and tools, and choosing the right tools and versions is a hurdle that might deter users from using Python applications.

An easier way to build an environment is through Anaconda, which provides a complete, precompiled technology stack for all users, including non-Python experts such as data analysts and students. For Anaconda installation instructions, see the Anaconda install documentation. The Snowflake SQLAlchemy package can then be installed on top of Anaconda using pip.

For more information, see the following documentation:

Installing Snowflake SQLAlchemy

The Snowflake SQLAlchemy package can be installed from the public PyPI repository using pip:

pip install --upgrade snowflake-sqlalchemy
Copy

pip automatically installs all required modules, including the Snowflake Connector for Python.

Note that the developer notes are hosted with the source code on GitHub.

Verifying your installation

  1. Create a file (e.g. validate.py) that contains the following Python sample code, which connects to Snowflake and displays the Snowflake version:

    #!/usr/bin/env python
    from sqlalchemy import create_engine
    
    engine = create_engine(
        'snowflake://{user}:{password}@{account_identifier}/'.format(
            user='<user_login_name>',
            password='<password>',
            account_identifier='<account_identifier>',
        )
    )
    try:
        connection = engine.connect()
        results = connection.execute('select current_version()').fetchone()
        print(results[0])
    finally:
        connection.close()
        engine.dispose()
    
    Copy
  2. Replace <user_login_name>, <password>, and <account_identifier> with the appropriate values for your Snowflake account and user. For more details, see Connection Parameters (in this topic).

  3. Execute the sample code. For example, if you created a file named validate.py:

    python validate.py
    
    Copy

The Snowflake version (e.g. 1.6.0) should be displayed.

Snowflake-specific parameters and behavior

As much as possible, Snowflake SQLAlchemy provides compatible functionality for SQLAlchemy applications.

For information on using SQLAlchemy, see the SQLAlchemy documentation.

However, Snowflake SQLAlchemy also provides Snowflake-specific parameters and behavior, which are described in the following sections.

Connection parameters

Required parameters

Snowflake SQLAlchemy uses the following connection string syntax to connect to Snowflake and initiate a session:

'snowflake://<user_login_name>:<password>@<account_identifier>'
Copy

Where:

  • <user_login_name> is the login name for your Snowflake user.

  • <password> is the password for your Snowflake user.

  • <account_identifier> is your account identifier. See Configuring a client, driver, library, or third-party application to connect to Snowflake.

    Note

    Do not include the snowflakecomputing.com domain name as part of your account identifier. Snowflake automatically appends the domain name to your account identifier to create the required connection.

Additional connection parameters

You can optionally include the following additional information at the end of the connection string (after <account_name>):

'snowflake://<user_login_name>:<password>@<account_identifier>/<database_name>/<schema_name>?warehouse=<warehouse_name>&role=<role_name>'
Copy

Where:

  • <database_name> and <schema_name> are the initial database and schema for the Snowflake session, separated by forward slashes (/).

  • warehouse=<warehouse_name> and role=<role_name>' are the initial warehouse and role for the session, specified as parameter strings, separated by question marks (?).

Note

After login, the initial database, schema, warehouse, and role specified in the connection string can always be changed for the session.

Proxy server configuration

Proxy server parameters are not supported. Instead, use the supported environment variables to configure a proxy server. For information, see Using a proxy server.

Connection string examples

The following example calls the create_engine method with the user name testuser1, password 0123456, account identifier myorganization-myaccount, database testdb, schema public, warehouse testwh, and role myrole:

from sqlalchemy import create_engine
engine = create_engine(
    'snowflake://testuser1:0123456@myorganization-myaccount/testdb/public?warehouse=testwh&role=myrole'
)
Copy

For convenience, you can use the snowflake.sqlalchemy.URL method to construct the connection string and connect to the database. The following example constructs the same connection string from the previous example:

from snowflake.sqlalchemy import URL
from sqlalchemy import create_engine

engine = create_engine(URL(
    account = 'myorganization-myaccount',
    user = 'testuser1',
    password = '0123456',
    database = 'testdb',
    schema = 'public',
    warehouse = 'testwh',
    role='myrole',
))
Copy

Opening and closing a connection

Open a connection by executing engine.connect(); avoid using engine.execute().

# Avoid this.
engine = create_engine(...)
engine.execute(<SQL>)
engine.dispose()

# Do this.
engine = create_engine(...)
connection = engine.connect()
try:
    connection.execute(<SQL>)
finally:
    connection.close()
    engine.dispose()
Copy

Note

Make certain to close the connection by executing connection.close() before engine.dispose(); otherwise, the Python Garbage collector removes the resources required to communicate with Snowflake, preventing the Python connector from closing the session properly.

If you plan to use explicit transactions, you must disable the AUTOCOMMIT execution option in SQLAlchemy.

For more information, see AUTOCOMMIT execution option in SQLAlchemy..

By default, SQLAlchemy enables this option. When this option is enabled, INSERT, UPDATE, and DELETE statements are committed automatically upon execution, even when these statements are run within an explicit transaction.

To disable AUTOCOMMIT, pass autocommit=False to the Connection.execution_options() method. For example:

# Disable AUTOCOMMIT if you need to use an explicit transaction.
with engine.connect().execution_options(autocommit=False) as connection:

  try:
    connection.execute("BEGIN")
    connection.execute("INSERT INTO test_table VALUES (88888, 'X', 434354)")
    connection.execute("INSERT INTO test_table VALUES (99999, 'Y', 453654654)")
    connection.execute("COMMIT")
  except Exception as e:
    connection.execute("ROLLBACK")
  finally:
    connection.close()

engine.dispose()
Copy

Auto-increment behavior

Auto-incrementing a value requires the Sequence object. Include the Sequence object in the primary key column to automatically increment the value as each new record is inserted. For example:

t = Table('mytable', metadata,
    Column('id', Integer, Sequence('id_seq'), primary_key=True),
    Column(...), ...
)
Copy

Object name case handling

Snowflake stores all case-insensitive object names in uppercase text. In contrast, SQLAlchemy considers all lowercase object names to be case-insensitive. Snowflake SQLAlchemy converts the object name case during schema-level communication (i.e. during table and index reflection). If you use uppercase object names, SQLAlchemy assumes they are case-sensitive and encloses the names with quotes. This behavior will cause mismatches against data dictionary data received from Snowflake, so unless identifier names have been truly created as case sensitive using quotes (e.g. "TestDb"), all lowercase names should be used on the SQLAlchemy side.

Index support

Indexes are supported only for Hybrid Tables in Snowflake SqlAlchemy. For more details on limitations and use cases, refer to Create Index documentation. You can create an index using the following methods:

  • Single column index

    You can create a single column index by setting the index=True parameter on the column or by explicitly defining an Index object.

    hybrid_test_table_1 = HybridTable(
      "table_name",
      metadata,
      Column("column1", Integer, primary_key=True),
      Column("column2", String, index=True),
      Index("index_1","column1", "column2")
    )
    
    metadata.create_all(engine_testaccount)
    
    Copy
  • Multi-column index

    For multi-column indexes, you define the Index object specifying the columns that should be indexed.

    hybrid_test_table_1 = HybridTable(
      "table_name",
      metadata,
      Column("column1", Integer, primary_key=True),
      Column("column2", String),
      Index("index_1","column1", "column2")
    )
    
    metadata.create_all(engine_testaccount)
    
    Copy

Numpy data type support

Snowflake SQLAlchemy supports binding and fetching NumPy data types. Binding is always supported. To enable fetching NumPy data types, add numpy=True to the connection parameters.

The following NumPy data types are supported:

  • numpy.int64

  • numpy.float64

  • numpy.datetime64

The following example shows the round trip of numpy.datetime64 data:

import numpy as np
import pandas as pd
engine = create_engine(URL(
    account = 'myorganization-myaccount',
    user = 'testuser1',
    password = 'pass',
    database = 'db',
    schema = 'public',
    warehouse = 'testwh',
    role='myrole',
    numpy=True,
))

specific_date = np.datetime64('2016-03-04T12:03:05.123456789Z')

with engine.connect() as connection:
    conenction.exec_sql_query(
        "CREATE OR REPLACE TABLE ts_tbl(c1 TIMESTAMP_NTZ)")
    connection.exec_sql_query(
        "INSERT INTO ts_tbl(c1) values(%s)", (specific_date,)
    )
    df = pd.read_sql_query("SELECT * FROM ts_tbl", connection)
    assert df.c1.values[0] == specific_date
Copy

Cache column metadata

SQLAlchemy provides the runtime inspection API to get the runtime information about the various objects. One of the common use case is get all tables and their column metadata in a schema in order to construct a schema catalog.

For more information, see runtime inspection API. For an example managing database schema migrations with SQLAlchemy, alembic .

A pseudo code flow is as follows:

inspector = inspect(engine)
schema = inspector.default_schema_name
for table_name in inspector.get_table_names(schema):
    column_metadata = inspector.get_columns(table_name, schema)
    primary_keys = inspector.get_primary_keys(table_name, schema)
    foreign_keys = inspector.get_foreign_keys(table_name, schema)
    ...
Copy

In this flow, a potential problem is it may take quite a while as queries run on each table. The results are cached but getting column metadata is expensive.

To mitigate the problem, Snowflake SQLAlchemy takes a flag cache_column_metadata=True such that all of column metadata for all tables are cached when get_table_names is called and the rest of get_columns, get_primary_keys and get_foreign_keys can take advantage of the cache.

engine = create_engine(URL(
    account = 'myorganization-myaccount',
    user = 'testuser1',
    password = 'pass',
    database = 'db',
    schema = 'public',
    warehouse = 'testwh',
    role='myrole',
    cache_column_metadata=True,
))
Copy

Note

Memory usage will go up higher as all of column metadata are cached associated with Inspector object. Use the flag only if you need to get all of column metadata.

VARIANT, ARRAY, and OBJECT support

Snowflake SQLAlchemy supports fetching VARIANT, ARRAY and OBJECT data types. All types are converted into str in Python so that you can convert them to native data types using json.loads.

This example shows how to create a table including VARIANT, ARRAY, and OBJECT data type columns:

from snowflake.sqlalchemy import (VARIANT, ARRAY, OBJECT)
...
t = Table('my_semi_structured_datatype_table', metadata,
    Column('va', VARIANT),
    Column('ob', OBJECT),
    Column('ar', ARRAY))
metdata.create_all(engine)
Copy

In order to retrieve VARIANT, ARRAY, and OBJECT data type columns and convert them to the native Python data types, fetch data and call the json.loads method as follows:

import json
connection = engine.connect()
results = connection.execute(select([t]))
row = results.fetchone()
data_variant = json.loads(row[0])
data_object  = json.loads(row[1])
data_array   = json.loads(row[2])
Copy

CLUSTER BY support

Snowflake SQLAlchemy supports the CLUSTER BY parameter for tables. For information about the parameter, see CREATE TABLE.

This example shows how to create a table with two columns, id and name, as the clustering key:

t = Table('myuser', metadata,
    Column('id', Integer, primary_key=True),
    Column('name', String),
    snowflake_clusterby=['id', 'name'], ...
)
metadata.create_all(engine)
Copy

Alembic support

Alembic is a database migration tool on top of SQLAlchemy. Snowflake SQLAlchemy works by adding the following code to alembic/env.py so that Alembic can recognize Snowflake SQLAlchemy.

from alembic.ddl.impl import DefaultImpl

class SnowflakeImpl(DefaultImpl):
    __dialect__ = 'snowflake'
Copy

See Alembic Documentation for general usage.

Key pair authentication support

Snowflake SQLAlchemy supports key pair authentication by leveraging the functionality of Snowflake Connector for Python. See Using key-pair authentication and key-pair rotation for steps to create the private and public keys.

The private key parameter is passed through connect_args as follows:

...
from snowflake.sqlalchemy import URL
from sqlalchemy import create_engine

from cryptography.hazmat.backends import default_backend
from cryptography.hazmat.primitives import serialization

with open("rsa_key.p8", "rb") as key:
    p_key= serialization.load_pem_private_key(
        key.read(),
        password=os.environ['PRIVATE_KEY_PASSPHRASE'].encode(),
        backend=default_backend()
    )

pkb = p_key.private_bytes(
    encoding=serialization.Encoding.DER,
    format=serialization.PrivateFormat.PKCS8,
    encryption_algorithm=serialization.NoEncryption())

engine = create_engine(URL(
    account='abc123',
    user='testuser1',
    ),
    connect_args={
        'private_key': pkb,
        },
    )
Copy

Where PRIVATE_KEY_PASSPHRASE is a passphrase to decrypt the private key file, rsa_key.p8.

The snowflake.sqlalchemy.URL method does not support private key parameters.

Merge command support

Snowflake SQLAlchemy supports performing an upsert with its MergeInto custom expression. See MERGE for full documentation.

Use it as follows:

from sqlalchemy.orm import sessionmaker
from sqlalchemy import MetaData, create_engine
from snowflake.sqlalchemy import MergeInto

engine = create_engine(db.url, echo=False)
session = sessionmaker(bind=engine)()
connection = engine.connect()

meta = MetaData()
meta.reflect(bind=session.bind)
t1 = meta.tables['t1']
t2 = meta.tables['t2']

merge = MergeInto(target=t1, source=t2, on=t1.c.t1key == t2.c.t2key)
merge.when_matched_then_delete().where(t2.c.marked == 1)
merge.when_matched_then_update().where(t2.c.isnewstatus == 1).values(val = t2.c.newval, status=t2.c.newstatus)
merge.when_matched_then_update().values(val=t2.c.newval)
merge.when_not_matched_then_insert().values(val=t2.c.newval, status=t2.c.newstatus)
connection.execute(merge)
Copy

CopyIntoStorage support

Snowflake SQLAlchemy supports saving tables and query results into different Snowflake stages, Azure Containers, and AWS buckets with its custom CopyIntoStorage expression. See COPY INTO <location> for full documentation.

Use it as follows:

from sqlalchemy.orm import sessionmaker
from sqlalchemy import MetaData, create_engine
from snowflake.sqlalchemy import CopyIntoStorage, AWSBucket, CSVFormatter

engine = create_engine(db.url, echo=False)
session = sessionmaker(bind=engine)()
connection = engine.connect()

meta = MetaData()
meta.reflect(bind=session.bind)
users = meta.tables['users']

copy_into = CopyIntoStorage(from_=users,
                            into=AWSBucket.from_uri('s3://my_private_backup').encryption_aws_sse_kms('1234abcd-12ab-34cd-56ef-1234567890ab'),
                            formatter=CSVFormatter().null_if(['null', 'Null']))
connection.execute(copy_into)
Copy

Iceberg Table with Snowflake Catalog support

Snowflake SQLAlchemy supports Iceberg Tables with the Snowflake Catalog, along with various related parameters. For detailed information about Iceberg Tables, refer to the Snowflake CREATE ICEBERG documentation.

To create an Iceberg Table using Snowflake SQLAlchemy, you can define the table using the SQLAlchemy Core syntax as follows:

table = IcebergTable(
        "myuser",
        metadata,
        Column("id", Integer, primary_key=True),
        Column("name", String),
        external_volume=external_volume_name,
        base_location="my_iceberg_table",
  as_query="SELECT * FROM table"
    )
Copy

Alternatively, you can define the table using a declarative approach:

class MyUser(Base):
    __tablename__ = "myuser"

    @classmethod
    def __table_cls__(cls, name, metadata, *arg, **kw):
        return IcebergTable(name, metadata, *arg, **kw)

    __table_args__ = {
        "external_volume": "my_external_volume",
        "base_location": "my_iceberg_table",
  "as_query": "SELECT * FROM table",
    }

    id = Column(Integer, primary_key=True)
    name = Column(String)
Copy

Hybrid Table support

Snowflake SQLAlchemy supports Hybrid Tables with indexes. For detailed information refer to the Snowflake CREATE HYBRID TABLE documentation.

To create a Hybrid Table and add an index, you can use the SQLAlchemy Core syntax as follows:

table = HybridTable(
    "myuser",
    metadata,
    Column("id", Integer, primary_key=True),
    Column("name", String),
    Index("idx_name", "name")
Copy

Alternatively, you can define the table using the declarative approach:

class MyUser(Base):
    __tablename__ = "myuser"

    @classmethod
    def __table_cls__(cls, name, metadata, *arg, **kw):
        return HybridTable(name, metadata, *arg, **kw)

    __table_args__ = (
        Index("idx_name", "name"),
    )

    id = Column(Integer, primary_key=True)
    name = Column(String)
Copy

Dynamic Tables support

Snowflake SQLAlchemy supports Dynamic Tables. For detailed information refer to the Snowflake CREATE DYNAMIC TABLE documentation.

To create a Dynamic Table, you can use the SQLAlchemy Core syntax as follows:

 dynamic_test_table_1 = DynamicTable(
       "dynamic_MyUser",
       metadata,
       Column("id", Integer),
       Column("name", String),
       target_lag=(1, TimeUnit.HOURS), # Additionally you can use SnowflakeKeyword.DOWNSTREAM
       warehouse='test_wh',
refresh_mode=SnowflakeKeyword.FULL
       as_query="SELECT id, name from MyUser;"
   )
Copy

Additionally you can define a table without columns using SqlAlchemy select() construct:

 dynamic_test_table_1 = DynamicTable(
       "dynamic_MyUser",
       metadata,
       target_lag=(1, TimeUnit.HOURS),
       warehouse='test_wh',
refresh_mode=SnowflakeKeyword.FULL
       as_query=select(MyUser.id, MyUser.name)
   )
Copy

Note

  • Defining a primary key in a Dynamic Table is not supported, meaning declarative tables don’t support Dynamic Tables.

  • When using the as_query parameter with a string, you must explicitly define the columns. However, if you use the SQLAlchemy select() construct, you don’t need to explicitly define the columns.

  • Direct data insertion into Dynamic Tables is not supported.