Re: [Zsqlml-users] some questions about coding zsqml selects

Hi Mathew,

To begin the answer to your question, I should explain the initial context 
for developing the zsqlml DTD. I wanted to define the structure of a RDBMS 
independently of SQL - a little like UML abstracts C++ / Java (I know that 
this is a simplistic analogy - please forgive:). Therefore the DTD defines 
the structural elements, and provides a means for converting this 
structure into vendor-specific SQL variants through its XSLT stylesheets.

As I understand it, you wish to use the zsqlml DTD to build the SELECT 
query. This is possible, but todate, the <zsql:select/> tag supports only 
a subset of possibility - it was included to support the definition of 
VIEWs.

I guess that the DTD could be ammended to extend the meaning of 
<zsql:command/> to allow for sub-element processing, specifically 
<zsql:field/>'s in your example. This is not a big deal.

The second question, encoding of the WHERE statement, appears to be 
correct. To check, run your zsqlml script through the transformer and 
inspect the resultant SQL.

Your third question relates to joining data across multiple databases - 
can this be supported by the database server? Ultimately, the zsqlml is 
transformed into SQL, so if its in SQL, it can be defined in zsqlml. 

So, to wrap up, I think that zsqlml can be used for your task, with a 
couple of minor tweaks. Work has me busy at the present, but I'll see if I 
can make the time. I'd obviously really appreciate help with the MySQL 
generator - it should / could be a simple edit on the existing pgsql 
XSLT;)

Regards, and thanks for expressing an interest in zsqlml
Adrian





Matthew Leingang <lei...@ma...>
Sent by: zsq...@li...
26/07/2002 17:26
Please respond to Matthew Leingang

 
        To:     <zsq...@li...>
        cc: 
        Subject:        [Zsqlml-users] some questions about coding zsqml selects

Hi,

I just downloaded zsqml because I'm looking for an SQL DTD to join some 
database applications via XML.  The only database I'm interested in is 
MySQL, which you don't support yet, but I might be able to help you with 
that.

Say I'm interested in writing the following in zsqlml:

SELECT user.id, CONCAT(person.firstname, ' ', person.lastname)
  FROM person, user
 WHERE person.user_id = user.id

I'm not sure how to code the CONCAT function.  I assume the WHERE clause 
would go something like

<zsql:where>
 <zsql:eq>
  <zsql:field table="person" column="user_id"/>
  <zsql:field table="user" column="id"/>
 </zsql:eq>
</zsql:where>

But I'm not sure. 

The next question:  Can I use zsqlml to join fields from different 
databases?  That doesn't seem to be the case.

Thanks for any help.

--Matthew Leingang

-- 
----------------------------------------------------------------
Matthew Leingang                http://www.math.rutgers.edu/
Rutgers University              lei...@ma...
Department of Mathematics       "This signature needs no quote."



-------------------------------------------------------
This sf.net email is sponsored by:ThinkGeek
Welcome to geek heaven.
http://thinkgeek.com/sf
_______________________________________________
Zsqlml-users mailing list
Zsq...@li...
https://lists.sourceforge.net/lists/listinfo/zsqlml-users