Re: [Haskelldb-users] HaskellDB in an industrial environment

[Bjorn B. <d00...@dt...>]

Frederik Eaton wrote:
>>Santoemma Enrico wrote:
>>
>>>1) Is the library too young for a real world project? Does it work
>>>with Oracle (throuhg ODBC)?
>>
>>There are still significant bugs in HaskellDB, see the open bugs in
>>http://sourceforge.net/tracker/?group_id=3D101095&atid=3D629040
>=20
>=20
> What's the biggest bug? "No explicit grouping"?

I'm not sure. AFAIK, there are no bugs which make HaskellDB generally=20
unusable, but different people will have different needs. Actually now=20
tha you mention it "No explicit grouping" feels more like a request for=20
enhancement, which are tracked by the RFE tracker at:

http://sourceforge.net/tracker/?group_id=3D101095&atid=3D629043

The bugs I personally think are the worst are the high priority ones in=20
the bug tracker.


> Also, it would be nice to have somewhere -- maybe in the wiki? -- some
> examples of SQL queries which can be done and which can't be done in
> HaskellDB. I have a program which I've started writing using regular
> SQL statements, and I'm wondering if I should translate it to
> HaskellDB. Something like this would help me decide. For example here
> are some queries, variables with $ represent parameters... (it's a
> simple flash card program)

I don't have time to write the HaskellDB code for you right now, it=20
being Saturday night and all, but see the comments below.

> select id from cards where cards.id not in
>     (select alg_data.id from alg_data) order by rand() limit 1

HaskellDB does not currently support queries in expressions, as needed=20
by the IN operator, see the RFE:
http://sourceforge.net/tracker/index.php?func=3Ddetail&aid=3D961869&group=
_id=3D101095&atid=3D629043

There is also no rand() function, but that can quite easily be added by=20
the used.

> select id from alg_data where uid =3D $uid and
>     when_eligible < $vt and
>     id like $pat order by curr_delay desc limit 1

Should be ok.

> select max(show_num) from hist where (uid,id)=3D($uid,$id)

Seems easy enough.

> select min(a.s), avg(a.s), max(a.s), sum(a.s) from=20
>     (select id,max(show_num) s from hist where=20
>             uid =3D $uid and
>             id in (select id from alg_data where
>                           uid=3D$uid and when_eligible < $vt)
>                    group by id) as a

IN expressions are not supported, see above. This query could be done as=20
a join instead, right? (It's saturday night, you don't expect me to=20
actually think, do you? :-P )

> P.S. Is there just the tutorial in wiki-form? Why not put the rest of
> the documentation on a wiki, so people can add to it?

Good idea! If you move the stuff to the wiki, I'll update the HaskellDB=20
homepage. Assuming there are no objections from anyone?

> P.P.S. The test application says "Server error!"...
>=20
> http://jackass.tekno.chalmers.se/dp03-7/cgi/run

Eh, right. The Chalmers computer support group seems to have changed the=20
installation. I have removed the link from the homepage. Maybe we can=20
put a demo app somewhere else, or link to an existing one. Shae?


/Bj=F6rn