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Re: Odbc and client library/drivers

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björn lundin (b.f.lundin@gmail.com) writes:
>>But you should not use SELECT * in production code.
> 
> Why?

Because if the table changes, that changes the result set, and 
"interesting" things can happen.

If you only need three columns, but retrieve 30 you are degrading 
performance in two way:
1) Extra chatter on the wire (particularly evil if you have LOB columns)
2) With a narrow result set, the optimizer might find a better query
   plan, and for instance use a narrow result set.

 
> The system is in Ada, and being in Ada it is strongly typed. That means
> we use some kind of struct, with members that corresponds to the fields
> of a table. We want to fill the whole struct, because i project
> adaptions, they might want to use a field that we do not use in
> standard. And then, we find the quality of the system increases a whole
> lot, if we get all the data out, instead of just getting the data we
> want rigth now. 

And then the question arises: is this column really used for anything?
Maybe you want to drop the column. Maybe you want to redefine its
semantics. But you find that it is virtually impossible to tell. 


> select a,b,c, from d 
> are farr worse, since that tends to be
> 
> get(a,varA);
> get(c,varC);
> get(b,varB); <--fail because we got B first.
> 
> 
> This is mostly a problem in migrating old sites,
> since the select * method gets it right.
 
I have not programmed much with ODBC, but I'm somewhat skeptic that 
this is a behaviour of the driver. Can you repro this with a C++ 
program? Since you program in Ada, I assume that you have something
that sits between your Ada environment and ODBC, and this could be
the culprit.


-- 
Erland Sommarskog, SQL Server MVP, esquel@sommarskog.se

Links for SQL Server Books Online:
SQL 2008: http://msdn.microsoft.com/en-us/sqlserver/cc514207.aspx
SQL 2005: http://msdn.microsoft.com/en-us/sqlserver/bb895970.aspx

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Odbc and client library/drivers björn lundin <b.f.lundin@gmail.com> - 2012-09-18 10:48 -0700
  Re: Odbc and client library/drivers Erland Sommarskog <esquel@sommarskog.se> - 2012-09-18 21:57 +0200
    Re: Odbc and client library/drivers björn lundin <b.f.lundin@gmail.com> - 2012-09-18 13:24 -0700
      Re: Odbc and client library/drivers George Neuner <gneuner2@comcast.net> - 2012-09-19 11:46 -0400
      Re: Odbc and client library/drivers Erland Sommarskog <esquel@sommarskog.se> - 2012-09-19 21:16 +0200
        Re: Odbc and client library/drivers Gene Wirchenko <genew@ocis.net> - 2012-09-19 13:14 -0700
          Re: Odbc and client library/drivers björn lundin <b.f.lundin@gmail.com> - 2012-09-19 13:41 -0700
            Re: Odbc and client library/drivers björn lundin <b.f.lundin@gmail.com> - 2012-09-19 13:45 -0700
              Re: Odbc and client library/drivers björn lundin <b.f.lundin@gmail.com> - 2012-09-19 13:56 -0700
                Re: Odbc and client library/drivers björn lundin <b.f.lundin@gmail.com> - 2012-09-19 14:00 -0700
        Re: Odbc and client library/drivers björn lundin <b.f.lundin@gmail.com> - 2012-09-19 13:26 -0700
          Re: Odbc and client library/drivers Erland Sommarskog <esquel@sommarskog.se> - 2012-09-19 23:44 +0200
            Re: Odbc and client library/drivers björn lundin <b.f.lundin@gmail.com> - 2012-09-20 01:50 -0700
              Re: Odbc and client library/drivers Erland Sommarskog <esquel@sommarskog.se> - 2012-09-20 23:31 +0200
                Re: Odbc and client library/drivers björn lundin <b.f.lundin@gmail.com> - 2012-09-21 01:18 -0700
                Re: Odbc and client library/drivers bradbury9 <ray.bradbury9@gmail.com> - 2012-09-21 02:57 -0700
                Re: Odbc and client library/drivers björn lundin <b.f.lundin@gmail.com> - 2012-09-21 03:10 -0700
                Re: Odbc and client library/drivers björn lundin <b.f.lundin@gmail.com> - 2012-09-21 03:14 -0700
  Re: Odbc and client library/drivers rja.carnegie@gmail.com - 2012-09-19 16:57 -0700
    Re: Odbc and client library/drivers björn lundin <b.f.lundin@gmail.com> - 2012-09-20 01:58 -0700

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