Foreign Data Wrappers是PostgreSQL取得外部数据比较方便的功能扩展。

可以取得关系数据库的数据，比如Oracle,MySQL,ODBC.

还可以取得NOSQL数据库的数据。比如CouchDB，Redis

还可以直接访问text文本文件，csv文件。

还可以访问twitter的数据。等等。

可以说利用好这些功能后，我们就会减少很多关联数据的编码。

具体信息参考了wiki。

Foreign Data Wrappers

In 2003,a new extension called SQL/MED ("SQL Management of External Data") was added to the SQL standard. It is a standardized way of handling access to remote objects in SQL databases. In 2011,PostgreSQL 9.1 was released with a great support of this standard.

In a nutshell,you can now use various Foreign Data Wrappers (FDW) to connect a PostgreSQL Server to remote data stores. This page is an incomplete list of the Wrappers available right now. Another fdw list can be found at the PGXN website.

Please keep in mind that most of these wrappers are not officially supported by the PostgreSQL Global Development Group (PGDG) and that some of these projects are still in Beta version. Use carefully!

SQL Databases Wrappers

oracle_fdw

• source code
• install with PGXN

mysql_fdw

This extension implements a Foreign Data Wrapper for MySQL. It is supported on PostgreSQL 9.1 and above.

• source code
• install with PGXN
• example

tds_fdw

A wrapper for accessing Sybase and Microsoft SQL Server databases.

• source code

odbc_fdw

A wrapper for databases with an ODBC driver,including Oracle,DB2,Microsoft SQL Server,Sybase,Pervasive SQL,IBM Lotus Domino,PostgreSQL and desktop database products such as FileMaker and Microsoft Access:

• source code
• install with PGXN
• Using odbc_fdw on windows to query sql server (Postgres OnLine Journal March/April 2012)

NoSQL Databases Wrappers

couchdb_fdw

A wrapper for CouchDB

• source code
• install with PGXN

redis_fdw

A wrapper for Redis

• source code
• install with PGXN

File Wrappers

file_fdw

A CSV files wrapper. Delivered as an official extension of PostgreSQL 9.1

• documentation
• example
• Another example Postgres OnLine Journal May 2012

file_text_array_fdw

Another CSV wrapper

• source code
• How to use it Postgres OnLine Journal May 2012

file_fixed_length_record_fdw

Fixed-width flat file wrapper

• source code

Others

twitter_fdw

A wrapper fetching text messages from Twitter over the Internet and returning a table

• source code
• install with PGXN

ldap_fdw

Allows PostgreSQL to query an LDAP server and retrieve data from some pre-configured Organizational Unit

• source code
• install with PGXN

PGStrom

uses GPU devices to accelarate sequential scan on massive amount of records with complex qualifiers.

• http://wiki.postgresql.org/wiki/PGStrom

s3_fdw

Reads files located in Amazon S3

• source code
• install with PGXN

www_fdw

Allows to query different web services:

• source code
• documentation/examples
• install with PGXN

Multicorn Foreign Data Wrappers

Multicorn is an extension that allows FDWs to be written in Python

SQL Database Wrappers

multicorn.sqlalchemyfdw

This fdw can be used to access data stored in any database supported by the sqlalchemy python toolkit.

• documentation

File Wrappers

muticorn.fsfdw

This fdw can be used to access data stored in various files,in a filesystem. The files are looked up based on a pattern,and parts of the file's path are mapped to various columns,as well as the file's content itself.

• documentation

multicorn.csvfdw

This fdw can be used to access data stored in CSV files. Each column defined in the table will be mapped,in order,against columns in the CSV file.

• documentation

Others

multicorn.rssfdw

This fdw can be used to access items from an rss feed.

• documentation

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