SQL statement joining Oracle and MS SQL Server

I never seen this, but is it possible to have one SQL call 开发者_开发技巧join data from Oracle and SQl Server?

Yes, Oracle and SQL Server both have functionality that allows to connect to other databases, including different vendors. In Oracle terminology, it's a database link instance while on SQL Server it's called a Linked Server instance.

The syntax to reference the instance is different between Oracle and SQL Server though. IE:

Oracle:

SELECT t.*
  FROM table_name@database_link_instance t

SQL Server:

SELECT t.*
  FROM linked_server_instance_name.database_name.schema_name.table_name t

does MySQL support the linked server concept?

No, the closest MySQL has is the FEDERATED engine, which is only for connecting to remote MySQL instances.

PostgreSQL?

PostgreSQL has dblink. Last time I looked at dblink (pre-v9 release), it only could connect to other PostgreSQL instances.

Yes- both Oracle and SQL Server support the linked server concept. That allows you to reference the other server using a 4 part name. For example:

select  *
from    LocalDb.Schema.Table
cross join
        OracleLinkedServer.RemoteDb.RemoteSchema.RemoteTable