From the May 2012 Issue of Prestwood eMag

Delphi Using Data: Heterogeneous Joins in Delphi By Mike Prestwood

Posted 22 years ago on 8/21/2002 and updated 3/18/2003 Take Away: Heterogeneous Joins in Delphi: by Mike Benemelis. A heterogeneous join is when you join tables from two different SQL servers (or a server and a local table) within the same query. This short article will show you how to perform such queries using Delphi. KB100009

The Delphi 1.0 Database Application Developer’s Guide for performing a Heterogeneous join is not quite correct. The following was provided (in part) by Borland Technical Support:

To perform a heterogeneous join do the following.

1. For each server table, a connection must exist before the query is executed. A TDatabase can be used to establish the connection.
2. The SQL statement must use real Alias names, as set up in the BDE config file, Not the Database Name properties from a Tdatabase component.
3. The SQL syntax should be formatted as follows: a double quote, a colon, a real alias name, a colon, the table name, and a double quote. See the example below:
4. Leave the DatabaseName Property of the TQuery blank.

For Example:

Select A.VENDORNO, B.VENDORNO
From ":DBDEMOS:VENDORS" A, ":IBLOCAL:VENDORS" B
where A.VENDORNO = B.VENDORNO

I performed a query similar to the one above, using tables in an Oracle and MS SQL database. Both databases are on a windows NT 4.0 OS. The performance seemed slow, possibly due to the BDE having to bring the data down locally and to data translations.

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KB Post Contributed By Mike Prestwood:

Mike Prestwood is a drummer, an author, and creator of the PrestwoodBoards online community. He is the President & CEO of Prestwood IT Solutions. Prestwood IT provides Coding, Website, and Computer Tech services. Mike has authored 6 computer books and over 1,200 articles. As a drummer, he maintains play-drums.com and has authored 3 drum books. If you have a project you wish to discuss with Mike, you can send him a private message through his PrestwoodBoards home page or call him 9AM to 4PM PST at 916-726-5675 x205. Visit Profile