[Gdal-dev] Re: Problem using OGR and join-functionality: column names gone when creating a new shapefile?

[Neil Best]

Hi, Wolfgang.  I think if you look at my recent posts to the list you 
will see that we are experiencing similar difficulties, you and I.  I 
wanted to do the same thing, make a join permanent, the only difference 
is that my source data is a .shp and a .dbf, rather than related tables 
in an RDBMS.

Since I can't get it to work either I can't speak with much authority, 
but I think I can point out something about your problem with field 
names.  If you look at the section describing joins on the OGR SQL page 
you will see a detailed discussion of how column names in the SQL 
statement map to the output.  My guess is that OGR is trying to give you 
fully qualified column names (e.g. "flurstck_test.ich_weiss_was_nicht") 
and truncating them according to the .dbf conventions.  Try using some 
aliases in your SQL.  If you post your query and a minimal description 
of your columns to the list I can try to offer a suggestion.

What's interesting is that we are both running the same version under 
Debian, albeit I am using Ubuntu.  I don't know if this is significant 
or not, especially since I got the same results when I dropped back to 
1.2.6, but there it is . . .


Neil


wqual wrote:
> Hi list,
> yesterday, I found a very interesting page on the internet - manpage of OGR 
> SQL [1]. Wow, I thought - I can perfom JOINs on the command line. Using 
> the join-command as described in this manual combinded to the ogrinfo-command 
> clearly showed, that a join was performed.
> *But could I make this permanent?* 
> Within the next step, I used ogr2ogr with the same sql-expression. A new 
> shapefile was created, the desired column of the second theme was appended to 
> the table (ogr2ogr -f "ESRI Shapefile" testfile.shp ./ -sql "select ...."
> 
> However, I realised, that all the column names were gone, or to be more 
> precise, lost their names in favour of a new one. All column names of the 
> first shapefile "Flurstck_test.shp" were (re)-named to "flurstck_t" and the 
> new column of the second theme "flurstck_nr.shp" is named "flurstck_n" now.
> Also, the column definitions were all converted to "Real" except the column 
> that was appended (joined) to the table. This column is of type "String".
> 
> Is this a common (known problem)? I would be most grateful for some comments, 
> as I really would like to use this feature of ogr! Thanks in advance!
> 
> I am using gdal 1.3.2-2 on a Debian machine.
> 
> Best regards,
> Wolfgang
> 
> [1] www.remotesensing.org/gdal/ogr/ogr_sql.html