Wednesday, June 10, 2009

What is the difference between xHarbour SQLRDD and Harbour RDDSQL. ?

CCH : An interesting post by Mindaugas Kavaliauskas on 7th June 2009 "Harbour Project Main Developer List."

RDDSQL implements accessing SQL query result via RDD interface, i.e. you write a SQL query and you are able to reach result of a query using FIELDGET(), DBSKIP(), DBGOTO(), etc. All these function calls does not generates additional queries, it will operate on result
of the query you've asked for.

RDDSQL does not try to be a "transparent" sollution for DBF to SQL move, and does not try to emultate DBF specific operations (ex., DBAPPEND(), DBDELETE(), OrdCreate(), FLOCK(), etc.) via some unnatural SQL operations.

I want to discuss this in more detail. Many current RDDs for accessing SQL servers (ex. SQLRDD from tries to make a feeling you are working with DBF file, but not with SQL database.

SQL server does not support many features, ex. RECNO(), deleted flag, file locks, record locks. These RDDs are emulating these features to make feeling of DBF. DELETED() function is emulated by creating additional table columns to store delete flag. Some "hidden system"
tables are used to register locking operations and emulate record and file locks in DBF style. The idea of SQL query is also lost. If you do a simple loop

DBUSEAREA(, "select * from my_table")
somefunc( FIELD->some_sql_field )

"Transparent" DBF to SQL solutions usually will read SQL rows in portions, let's say 100 records per query. So, hidden queries are generated. If another client issues UPDATE query between these hidden queries, it can happen, that the same row will be fetched the second time, or does not fetched at all.

The idea of RDDSQL is different. It does not make hidden queries. All queries should be made explicitly by programmer. RDDSQL gives access to query result via RDD interface, it does not tries to emulate DBF and be "transparent" solution for DBF to SQL migration. If you

DBUSEAREA(, "select * from my_table")

the entire query (it could contain millions of records, so be carefull!) will be cached.

The features of RDDSQL approach are:
- It's possible to access SQL database of other applications. Other
applications usualy does not follow agreement of "transparent" SQL
drivers about additional DELETED column, _RECNO in the end of index
expression, etc. Access of SQL database of another applications is
sometimes not possible.

- It's query oriented. That means a simple DO WHILE ! EOF() loop will iterate each records once and only once. This is not true for "transparent" DBF to SQL solutions.


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Welcome to Clipper... Clipper... Clipper

In 1997, then using Delphi 3, I had already created 32-bits Windows applications for HRIS, ERP and CRM. In 2007, using Ruby on Rails, an AJAX powered CRM site running on Apache & MySQL was created and I am now using Visual Studio .Net 2008 to create web-based projects and Delphi 7 for Win32 applications using SQL2005 & DBFCDX.

So, why then am I reviving the Original Clipper... Clipper... Clipper via a Blog as CA-Clipper is a programming language for the DOS world ? Believe it or not, there are still some clients using my mission-critical CA-Clipper applications for DOS installed in the late 80's and up to the mid 90's. This is testimony to CA-Clipper's robustness as a language :-)

With the widespread introduction of Windows 7 64-bits as the standard O/S for new Windows based PCs & Notebooks, CA-Clipper EXE simply will not work and it has become imperative for Clipper programmers to migrate immediately to Harbour to build 32/64 bits EXEs

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You may ask, what is this Clipper stuff ? Could Clipper be something to do with sailing as it is the name of a very fast sailing American ship in the 19th century ?

Well, Clipper or to be precise, CA-Clipper is the premier PC-Software development tool for DOS. It was first developed by Nantucket Corporation initially as a compiler for dBase3+ programs. Since then, CA-Clipper has evolved away from its x-base roots with the introduction of lexical scoping & pre-defined objects like TBrowse. As at today, the most stable version ofClipper is 5.2e while the latest version, 5.3a was introduced on 21 May 1996.

As at 11th November, 1996, an unofficial 5.3a fixes file was made available by Jo French. See the About CA-Clipper 5.3a section for more details. BTW, Jo French uploaded the revised 5.3a fixes file on 20th November, 1996.

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The latest news is that CA has finally released the long-awaited 5.3b patch on 21 May, 1997.

For 5.3b users, you must a take a look at Jo French's comments on unfixed bugs in 5.3b.

BTW, have you used Click ? If you're a serious Clipperprogrammer and need an excellent code formatter, Click is a natural choice. How to get it ? Simple, access Phil Barnett's site via my Cool Clipper Sites.

32-bits Clipper for Windows ?

Have you tried Xbase ++ ? Well, I have and compared to Delphi (my current Windows programming tool of choice), I'm still sticking to Delphi.

Anyway, you should visit the Alaska Home Page. Give it a chance and then draw your own conclusions !.

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