[GRASS-user] Manage Sqlite Database columns

Johannes Radinger JRadinger at gmx.at
Sat Feb 4 02:48:00 EST 2012

Am 03.02.2012 um 17:30 schrieb Micha Silver:

> On 02/03/2012 01:57 PM, Johannes Radinger wrote:
>> Hello,
>> While working on a vectorfile (lines) with 46000 entries in sqlite in GRASS
>> some questions popped up:
>> 1) Somehow my cat column is double precision instead of integer...Can it be transformed into an integer within GRASS GIS to do some v.select operations with it? If yes, how exactly?
> Converting the values to integer can be done with the sqlite CAST(cat AS integer). But that probably won't help. THe column itself needs to be integer type, so I think you need to make a new cat column and populate it with integer values:
> Using sqlite:
> sqlite> alter table <your vector> add column cat2 integer;
> sqlite> update <your vector> set cat2=CAST(cat AS integer);

Thank you for that, but what should I use to call sqlite commands? Can that be done inside GRASS, is there any tool? Or should that be 
done from any sqlite-management software or from any command line programm (GRASS console? Mac Terminal?)

>> 2) Is it possible to change the order of the columns in the attribute table?
> In sqlite you can't change the order of the columns, so you'll need to create a new table ordered the way you want, then juggle the table names so that the grass vector "sees" the new reordered table.
> Suppose, after the first question above you have a vector with columns: 
>     cat double, label text, value double, cat2 integer
> and you want the reordered table to be: 
>     label, value, cat (the new integer one)

Of course it is not necessary to change the order for database calls etc. It would just be interesting when I look into the attribute
table of a vector within GRASS I have to scroll to the very far rigtht side to get to e.g. my vector name label which is not that comfortable
for a quick view... Therefore a quick sort (drag and drop) within the GRASS GUI would be of nice but not necessary of course...

> then:
> sqlite> CREATE TABLE tmp (label text, value double, cat integer);
> sqlite> INSERT INTO tmp (label, value, cat) SELECT label, value, cat2 FROM <your_vector>;
> sqlite> ALTER TABLE <your_vector> RENAME TO vector_bak;
> sqlite> ALTER TABLE tmp RENAME TO <your_vector>;
> HTH,
> Micha
>> I am working on GRASS GIS 6.5SVN on Mac OSX.
>> Best regards,
>> Johannes
> -- 
> Micha Silver
> GIS Consultant, Arava Development Co.
> http://www.surfaces.co.il

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