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From Christian Riedel <sa...@nurfuerspam.de>
Subject Re: Using derby to parse an SQL statement
Date Fri, 21 Nov 2008 10:53:45 GMT
Hi Rick,

as requested I want to report our findings when working with the parser:

Background: we want to use the parser to analyze SQL statements that are 
generated by different tools, for example an ETL tool. It seems that, 
depending on the DBMS the tools are configured to work with, the 
generated SQL is not completely standard conform, which causes a parser 

As example the statement

	select null "a_null_column", id "an_id_column" from a_table

runs fine on an MSSQL DB, but causes problems on a DB2.

Feeding the parser with this statement brings up a parsing exception. 
Supposedly because it is not SQL standard conform.

Our question is: Does the derby parser "only" understand standard SQL or 
can it be instructed to accept DB2, Oracle, MSSQL etc. specific syntax 
as well?

Other than this we have not had any problems with the parser. Using the 
Derby AST brings the information we wanted.

I hope you can help us with this problem as well.



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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