[Hsqldb-developers] Parser / extended SQL syntax

[Johannes v. S. <jvs...@we...>]

Hello everyone,

as I already posted on hsqldb-users (sorry wasn't aware of hsqldb-developers):


My question was:  Which parser hsqldb is using?
Is it javacc etc., or a parser you have developed yourself?

Whould it be possible to change the way hsqldb parses the sql, as for 
implementing an enhanced version of sql, with additional 
keywords/expressions etc?

The background:
I'm studying applied computer science in germany, and for my diploma 
thesis, I'm enhancing an application developed at our university 
(university of augsburg, http://www.uni-augsburg.de/).
This application is called Preference SQL, it enhances standard SQL 
with the notion of preferences.
One can for example state a query like
 SELECT * FROM usedcars
   WHERE make = 'Ford'
   PREFERRING price AROUND 20000
          AND HIGHEST(power)
          PRIOR TO color = 'red'
for which I guess the meaning is quite obvious.

The difference to standard SQL is that the conditions in the PREFFERING 
clause don't have to be matched exactely, but rather are treated as soft 
selections. So if there's no exact match, the best matching entries are 
returned. (I can give you more background about this if someone should 
be interested  :)  ).

Until now, the program is implemented in the way that a JDBC driver 
takes the PreferenceSQL statement, connects the the underlying 
(standard) sql database (oracle, mysql etc), fetches all the nessesary 
tables with hard selections (WHERE..), and executes the preference part 
of the query on this data.
To parse the query, we use a JavaCC generated parser.

My task would be to implement the exection of preference queries 
directly into a java database, and I was told to use your hsqldb.
So I would adapt the classes that do the parsing on the incoming query, 
so that they can handle the extended syntax.

My questions would be:
What do you think of that task and it's complexity?
How is your parser organized/what parser do you use?
Whould it be possible to convert our javacc parser to your parser format?
How much of the code would I have to change to implement execution of preference queries?

many thanks for your answers,

regards, Johannes

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