连接来自两个单独数据库的结果 [英] Joining Results from Two Separate Databases

问题描述

是否可以从两个独立的postgres数据库中JOIN行?

Is it possible to JOIN rows from two separate postgres databases?

我正在使用一台服务器中具有几个数据库的系统，有时我确实需要这样的功能.

I am working with system with couple databases in one server and sometimes I really need such a feature.

推荐答案

根据 http: //wiki.postgresql.org/wiki/FAQ

除了当前数据库外，没有其他方法可以查询数据库. 因为PostgreSQL加载特定于数据库的系统目录，所以它是 不确定跨数据库查询的行为. contrib/dblink允许使用函数调用进行跨数据库查询.的 当然，客户也可以同时连接到不同的 数据库并在客户端合并结果.

There is no way to query a database other than the current one. Because PostgreSQL loads database-specific system catalogs, it is uncertain how a cross-database query should even behave. contrib/dblink allows cross-database queries using function calls. Of course, a client can also make simultaneous connections to different databases and merge the results on the client side.

编辑:3年后(2014年3月)，此常见问题解答条目已被修改，对您的帮助更大:

EDIT: 3 years later (march 2014), this FAQ entry has been revised and is more helpful:

如何使用多个数据库执行查询?

除了当前数据库外，没有其他方法可以直接查询数据库 一.因为PostgreSQL加载特定于数据库的系统目录，所以它是 不确定跨数据库查询的行为方式.

There is no way to directly query a database other than the current one. Because PostgreSQL loads database-specific system catalogs, it is uncertain how a cross-database query should even behave.

PostgreSQL中的SQL/MED支持允许外部数据包装器"来 创建后，将远程数据库中的表链接到本地​​数据库. 远程数据库可能是同一PostgreSQL上的另一个数据库 实例或遍布全球的数据库，都没关系. postgres_fdw内置于PostgreSQL 9.3，包括读/写 支持;可以将9.2的只读版本编译并安装为 一个contrib模块.

The SQL/MED support in PostgreSQL allows a "foreign data wrapper" to be created, linking tables in a remote database to the local database. The remote database might be another database on the same PostgreSQL instance, or a database half way around the world, it doesn't matter. postgres_fdw is built-in to PostgreSQL 9.3 and includes read/write support; a read-only version for 9.2 can be compiled and installed as a contrib module.

contrib/dblink允许使用函数调用和跨数据库查询 适用于许多较旧的PostgreSQL版本.不像postgres_fdw 它无法将条件推送"到远程服务器，因此它经常 可以获取比您所需更多的数据.

contrib/dblink allows cross-database queries using function calls and is available for much older PostgreSQL versions. Unlike postgres_fdw it can't "push down" conditions to the remote server, so it'll often land up fetching a lot more data than you need.

当然，客户端也可以同时连接到 不同的数据库并将结果合并到客户端.

Of course, a client can also make simultaneous connections to different databases and merge the results on the client side.

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