RE: [mdb-dev] Segmentation Fault

[<br...@br...>]

Columns are never really removed.  So, you have a table with 10
columns and delete 3, and then add more rows, the new rows will have
10 columns not 7.  For fixed columns, the space used will be equal to
the length of the column (4 bytes for int's, 8 for datetime's, etc). 
For variable length columns, this will be 1 byte for JET3 or 2 bytes
for JET4.  So, not only does it use up one of the 255 "column slots"
it also uses space on disk.

Brian

On Thu, 15 Apr 2004 01:59:30 +0100, "Fergus Allan" wrote:

> 
> 
> When you say table definitions, you can add upto 255 columns.  This
> includes
> any deletions and additions.  Changes to the definitions are 'fixed'
> when
> any new data is added.
> 
> Thus
> 
> Add column
> add data
> delete column
> 
> repeated ~250 will leave you with a table with, say, 5 columns (what
> ever
> you stated with), but any attempt to add a column gives an error in
> Access
> that too many columns are defined.
> 
> 
> Regards
> 
> Fergus Allan
> 
> 
> 
> -----Original Message-----
> From: mdb...@li...
> [mailto:mdb...@li...]On Behalf Of
> br...@br...
> Sent: 15 April 2004 00:45
> To: in...@al...
> Cc: mdb...@li...
> Subject: Re: [mdb-dev] Segmentation Fault
> 
> 
> I'm currently working on these issues.  What happens is you have a
> table that has at some point had columns added or deleted from the
> table.  When this happens, Access does not go back and retouch the
> rows, it simply updates the table definition and moves on.  Thus the
> number of columns recorded for the table doesn't match the the number
> stamped on the row.  So what does this have to do with your problem?
> 
> version 0.5 largely ignored the issue and that works for a certain
> subset of column add/deletes, but can give screwy results in other
> cases (values appearing in the wrong column or corrupted for
> instance).  The CVS version is attempting to take a more correct
> approach, but isn't quite there yet.
> 
> I have a yet-to-be-checked-in patch to handle JET4 databases, but I'm
> not quite ready with JET3 (but very close).  I hope to have it all
> ready by this weekend.   If you're interested in testing, I'll let
you
> know when it's commited.
> 
> Brian
> 
> On Wed, 14 Apr 2004 15:48:37 -0600, "John Finlay" wrote:
> 
> >
> > I had successfully compiled mdbtools-0.5 and was using it to access
> > the .mdb
> > database I am working on successfully, but today when I compiled
> > mdbtools
> > from the CVS sources, it compiled 'successfully', however now every
> > time I
> > use any mdb-xxxx binaries to access the database, all display the
> same
> > result:
> >
> > I get 24 lines identical to the warning and then a segmentation
> fault.
> >
> > WARNING: number of table columns does not match number of row
> columns,
> > strange results may occur
> > Segmentation fault
> >
> > Just to verify that the mdb didn't become corrupt somehow, I tried
> the
> > 0.5
> > binaries and they still function correctly and I'm able to retrieve
> > data
> > from them. mdb-version identifies the mdb as Jet3 which is correct,
> but
> > outside of that I cannot get any useful information without
warnings
> > about
> > table columns not matching row columns and a segmentation fault.
> >
> > Has anyone else encountered this? Any ideas? System is Red Hat 9.0,
> > GLIB
> > 2.4.0, libtool-1.5, flex-2.5.4, bison-1.875, autoconf 2.59,
> > automake-1.8.3
> >
> > John Finlay
> > IT Systems Manager
> > Custom Linen Systems Ltd.
> > 2925 10th Avenue N.E.
> > Calgary, Alberta T2A 5L4
> > Email: in...@al...
> >
> >
> >
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