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From Christian Riedel <sa...@nurfuerspam.de>
Subject Re: Using derby to parse an SQL statement
Date Fri, 14 Nov 2008 08:10:28 GMT
Sorry, if this is a duplicate ... it seems my message was not delivered 
in the first place.

Hi Rick,

that sounds wonderfull! I haven't had the chance to try your changes 
today, though. I'll check it tomorrow right away.

Of course, I will report any insights / problems in Jira.

Thanks for your great support!


Rick Hillegas schrieb:
> Hi Christian,
> I have checked the patch into the development trunk. At this point, you 
> will automatically get the fix if you build an up-to-date copy of the 
> trunk. Please let us know what your experience is. You will notice from 
> the discussion on the JIRA that some syntax may not work--this is 
> because the separation between the parsing and name-resolution phases is 
> not as clean as it should be. The JIRA would be a good place for you to 
> record your observations.
> Thanks,
> -Rick
> Christian Riedel wrote:
>> Hi Rick,
>> at first thank you very much for your efforts so far. At a first 
>> glance your changes to the code seem to be exactly what we want. I 
>> will try if it works asap.
>> To test it with the derby libs I'd have to work on the current trunk 
>> and apply the patch an then compile derby manually, right?
>> I'll keep you updated
>> Thanks for your help
>> Christian
>> Rick Hillegas schrieb:
>>> Hi Christian,
>>> I have created a JIRA to track this issue: 
>>> https://issues.apache.org/jira/browse/DERBY-3946
>>> I have attached to the JIRA a small patch which exposes the AST 
>>> produced by the parser. I have also attached a simple program, 
>>> ASTParser, which shows how to retrieve the AST from Derby. I am 
>>> inclined to check this patch in to the trunk. Please let me know if 
>>> you find this useful and if you would like me to port this patch to 
>>> another Derby branch.
>>> Hope this helps,
>>> -Rick
>>> Christian Riedel wrote:
>>>> 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
>>>> Christian
>>>> 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"
>>>>>> la SELECT street AS "ADDRESS" FROM USER_DATA ).
>>>>>> 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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