SQLAlchemy Foreign Data Wrapper


This fdw can be used to access data stored in a remote RDBMS. Through the use of sqlalchemy, many different rdbms engines are supported.



You will need the sqlalchemy library, as well as a suitable dbapi driver for the remote database.

You can find a list of supported RDBMs, and their associated dbapi drivers and connection strings in the sqlalchemy dialects documentation.

Connection options

Connection options can be passed either with a db-url, or with a combination of individual connection parameters. If both a db_url and individual parameters are used, the parameters will override the value found in the db_url. In both cases, at least the drivername should be passed, either as the url scheme in the db_url or using the drivername parameter.


An sqlalchemy connection string. Examples:

  • mysql: mysql://<user>:<password>@<host>/<dbname>
  • mssql: mssql://<user>:<password>@<dsname>

See the sqlalchemy dialects documentation. for documentation.

The remote username.
The remote password
The remote host
The remote database
The remote port

Other options

tablename (required)
The table name in the remote RDBMS.
Identifies a column which is a primary key in the remote RDBMS. This options is required for INSERT, UPDATE and DELETE operations
The schema in which this table resides on the remote side

When defining the table, the local column names will be used to retrieve the remote column data. Moreover, the local column types will be used to interpret the results in the remote table. Sqlalchemy being aware of the differences between database implementations, it will convert each value from the remote database to python using the converter inferred from the column type, and convert it back to a postgresql suitable form.

What does it do to reduce the amount of fetched data ?

  • quals are pushed to the remote database whenever possible. This include simple operators :

    • equality, inequality (=, <>, >, <, <=, >=)
    • like, ilike and their negations
    • IN clauses with scalars, = ANY (array)
    • NOT IN clauses, != ALL (array)
  • the set of needed columns is pushed to the remote_side, and only those columns will be fetched.

Usage example

For a connection to a remote mysql database (you’ll need a mysql dbapi driver, such as pymysql):

CREATE SERVER alchemy_srv foreign data wrapper multicorn options (
    wrapper 'multicorn.sqlalchemyfdw.SqlAlchemyFdw'

create foreign table mysql_table (
  column1 integer,
  column2 varchar
) server alchemy_srv options (
  tablename 'table',
  db_url 'mysql://myuser:mypassword@myhost/mydb'