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From Christian Riedel <sa...@nurfuerspam.de>
Subject Re: Using derby to parse an SQL statement
Date Wed, 12 Nov 2008 15:46:16 GMT
Hi Rick,

first of all thanks for your answer ... now the relations have become a 
lot clearer ...

Your are right, there is a lot of things to be done that we probably 
don't want to go through. You asked why we cannot take the whole derby 
engine and use it ... well there is nor real reason not to do so. The 
only "problem" I see is, that derby is a dbms - if I am not mistaken - 
and we only have an SQL statement that we extract from a text file and 
want tot analyze it to extract some metadata from it.

So if we take the derby engine as it is, how can I prevent that we have 
to set up a "dummy" DB in order to be able to actually use thje parsing 
feature ....

I hope you see my point.

We could live with setting up a dummy DB ... and I do think that the 
derby AST offers all information we need. It's just that I don't see how 
we can set this thing up. So having a dummy DB is necessary to be able 
to intercept the parsing process to get hold of the AST? Can we actually 
access the AST if we choose to set up a dummy DB? I think that would be 
something we could live with ;-)

Thanks for your support


Rick Hillegas schrieb:
> Hi Christian,
> I think you will have difficulty isolating the Parser from the rest of 
> the SQL interpreter. In theory, you should be able to isolate the 
> compiler from the execution engine and the storage layer--but that is an 
> untested theory.
> The Parser wants to turn out abstract syntax trees (AST). Ideally, the 
> Parser would just need to ask a NodeFactory for AST nodes and you could 
> supply your own NodeFactory. But I think that there is a fair amount of 
> coupling between the Parser and Derby's concrete implementation of 
> NodeFactory. I think that you could uncouple the two, but you may not 
> want to spend your time on that.
> So the Parser is going to force you to pull in the AST nodes. Once you 
> do that, you will end up with the whole compiler. In particular, the AST 
> nodes (and the Parser itself) expect that you will supply an 
> implementation of LanguageConnectionContext, the master state variable 
> for the whole SQL interpreter. Untangling that requirement is another 
> chunk of work you may not want to do.
> Then there is the Monitor. It has been a while since I was in that code 
> but I seem to recall that fairly early on the Monitor wants to fault in 
> a storage layer. In theory you ought to be able to supply the Monitor a 
> list of modules that doesn't include a storage layer. But since no-one 
> runs in this configuration, there are probably a lot of undocumented 
> surprises that you may not want to fix either.
> Can I ask you what breaks if you just pull in the whole Derby engine? 
> Are you concerned that you will fault in too much code that you barely 
> use? Are you concerned that you'll end up with a dummy database that you 
> don't need? Are Derby's AST nodes not a usable representation of 
> statement syntax?
> Thanks,
> -Rick
> Christian Riedel wrote:
>> Hi there,
>> we are working on a small project where we need to analyze an SQL 
>> statement that can be of any kind: very simple, with inner selects, 
>> complex join etc.
>> We figured it inappropriate to start to write our own parser when 
>> there are other projects, like derby, out there that can do it much 
>> better than we would possibly do ... so this was our idea:
>> Can we use derby to create an instance of Parser 
>> (org.apache.derby.iapi.sql.compile.Parser.class) and let our SQL 
>> statement be parsed by calling the parse() method on this instance? 
>> What we want to have is a syntax tree of the statement that allows us 
>> to see which tables and which fields are accessed / included in the 
>> statement (including any possibly done "renames" รก la SELECT street AS 
>> The problem is, that we are stuck ... we spent several days now to try 
>> to find the proper way to create an instance of the Parser. Is it 
>> possible at all without having to set up a running derby system?
>> Is the Monitor class the right entry point? How can we create a 
>> CompilerContext so that a Parser instance can be created?
>> This sure is off-topic but we don't see any way through all this. Can 
>> you help us?
>> Thanks in advance
>> Christian

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