Is anyone else as annoyed as I am about the lack of multi-field joins in FOCUS databases? I had hoped this feature was introduced with XFOCUS, but it appears not.

This message has been edited. Last edited by: Francis Mariani,

I thought that multifield joins was coming in, in one of the later releases ?

I had hoped that a conditional join would work.

Seems to work for Loaded FOCUS files, but not Held FOCUS files.

JOIN FILE VIDEOTRK AT MOVIECODE TAG V1 TO ALL 
     FILE MOVIES   AT RELDATE   TAG M1 AS JW1
-*  WHERE DATEDIF(RELDATE, TRANSDATE,'Y') GT 10;
  WHERE V1.MOVIECODE EQ M1.MOVIECODE;
END
TABLE FILE VIDEOTRK

 PRINT LASTNAME
 TITLE
-*ON TABLE HOLD
END

There IS multi-field JOIN using MDI, plus there is external index.

Diligent use of these, together with intelligent partitions, provides excellent performance in a data mart application.

Alan, thanks for pointing me to MDI. I have some reading to do!

Multi-Dimensional Index (MDI)

Interesting reading...

This could be useful.

Sorry to throw an old spanner into the works.

XFOCUS as we all know requires a seperate licence.

But did you know that the multi-dimensional indexing functionality

requires yet another additional licence.

You can have the first without the second but not the second without the first.

That does seem interesting indeed! What I can't gather from the documentation though is how you would create a HOLD file with an MDI?

Say we have:

TABLE FILE CAR
PRINT *
BY COUNTRY
BY CAR
ON TABLE HOLD AS foo FORMAT XFOCUS
END

How would you add an MDI index to that? Can that be done during the creation of the HOLD-file or does it require a separate REBUILD command? What would that look like?

From the doc:

Building and Maintaining a Multi-Dimensional Index
The REBUILD command is used to create or maintain a multi-dimensional index. This command can be issued in a FOCEXEC.

The best MDI is built by specifying the dimensions in order of best cardinality (most distinct values).

To issue the REBUILD command in a FOCEXEC, you place the REBUILD command and the user-supplied information needed for REBUILD processing in the FOCEXEC.

If the MDI file might be larger than two gigabytes or if you plan to add more data partitions to it, the MDI index file must be partitioned from the initial REBUILD phase. After the index has been created, you can use it in a retrieval request. You cannot use an MDI for modifying the data source. If you update the data source without rebuilding the MDI and then attempt to retrieve data with it, WebFOCUS displays a message indicating that the MDI is out of date. You must then rebuild the MDI.

I wonder how many people have tried MDI - I don't think I've ever seen a comment about it on FocalPoint.

The reason I asked was that it isn't clear to me from the docs what such a REBUILD command would look like. I even checked the docs about REBUILD and although that does contain an example, it contains no explanation of what the example achieves.

I often have this problem with the help-files BTW - either they end just when things get interesting, or they show some example that make you go "Huh, wot?!?" and leave it at that. I get the impression that the people responsible for the documentation much rather have us pay for a course than actually understand things from the docs. Not that I mind taking a meaningful course if I get offered one.

Regarding never hearing about MDI before, I can entirely imagine people reading "MDI" and thinking it's about: http://en.wikipedia.org/wiki/M...e_document_interface (where I have to add that I think the section about advantages/disadvantages isn't done very well).

I agree with you completely regarding WF documentation. I once posted a question/comment of FP regarding the lack of JSP examples for the ReportCaster API and someone named "Gerry" responded stating there indeed was one example, though without any explanation of the code. It's very frustrating.

I always thought MDI meant "Modern Demolition Initiation", but I now realize there are many meanings.

More Licenses !