[gdal-dev] Still not working: Python ogr DataSource.ExecuteSQL syntax?

[Homme Zwaagstra]

Dave,

Try the following modified version of your code snippet below. Note
that `ExecuteSQL` expects a simple SQL string - it does not do any
interpretation of local python variables! See
http://www.gdal.org/ogr/ogr_sql.html for more information on the SQL.

    import os
    from osgeo import ogr
    ogr.UseExceptions()         # if something goes wrong, we want to know about it
    driver = ogr.GetDriverByName('ESRI Shapefile')
    ds = driver.Open('three_points.shp', 0)#0--read-only
    layer = ds.GetLayer()
    layerName =  layer.GetName() #returns string 'three_points'
    test = ds.ExecuteSQL('select * from "%s"' % layerName)

Cheers,

Homme

On Tue, Feb 05, 2013 at 12:39:50AM -0900, David Verbyla wrote:
> I am not understanding some key aspect of this function.
> For example:
> #three_points.shp contains
> #Class, Point_X, Point_Y
> # 1,301665.4,1701522.8
> # 2,302240.3,1701992.1
> # 3,301559.8,1701112.1
> import os
> from osgeo import ogr
> driver = ogr.GetDriverByName('ESRI Shapefile')
> ds = driver.Open('three_points.shp',0)#0--read-only
> layer = ds.GetLayer()
> layerName =  layer.GetName() #returns string 'three_points'
> test = ds.ExecuteSQL('select from layerName *')
> print type(test) #returns <type 'NoneType'>
> 
> test = ds.ExecuteSQL('select from layer.GetName')
> print type(test) #returns <type 'NoneType'>
> 
> ds.ExecuteSQL('select from layerName where Class > 0')
> print type (test) #returns <type 'NoneType'>
> 
> Thanks in advance.
> 
> Dave Verbyla
> 
> 
> On Mon, Feb 4, 2013 at 11:59 PM, Homme Zwaagstra <hrz at geodata.soton.ac.uk>wrote:
> 
> > Hello Dave,
> >
> > On Mon, Feb 04, 2013 at 06:32:11PM -0900, David Verbyla wrote:
> > > I am trying to figure out the syntax for .ExecuteSQL using Python ogr.
> >
> > I have successfully been using `DataSource.ExecuteSQL` from Python
> > using gdal 1.9.0.
> >
> > > For example:
> > > fireLayer.SetAttributeFilter(None) #returns all 2623 polygons
> > > fireLayer.SetAttributeFilter(" FIREID < 75 ") #returns 4 polygons
> > >
> > > I am trying to get the same results using the ExecuteSQL:
> > > testLayer = dataSource.ExecuteSQL("select * from fireLayer")
> > > type(testLayer) #retuns NoneType
> > > testLayer = dataSource.ExecuteSQL("select * from fireLayer where FIREID <
> > > 75")
> > > type(testLayer) #retuns NoneType
> >
> > `None` seems to be returned when the SQL does not generate any
> > features.  Therefore the only thing I can think that might be wrong is
> > that the identifier `fireLayer` in the SQL above is not matching the
> > layer name in `dataSource`. Amending to the following *should* work:
> >
> >     dataSource.ExecuteSQL('select * from "%s"' % fireLayer.GetName())
> >
> > Cheers,
> >
> > Homme
> >
> > > Thanks in advance.
> > >
> > > Dave Verbyla
> > >
> > > On Sat, Dec 22, 2012 at 7:17 AM, David Verbyla <dlverbyla at alaska.edu>
> > wrote:
> > >
> > > >
> > > > I am a newbie to OGR/OSR using Python 2.7.2, please excuse my
> > ignorance:
> > > >> I am trying to find the distance to the closest polygon for each
> > point.
> > > >> Is there a more efficient way than simply computing the distance to
> > all
> > > >> polygons for each point?  For example:
> > > >>
> > > >
> > > > nPts = pointsLayer.GetFeatureCount()
> > > > nPolys = polysLayer.GetFeatureCount()
> > > >
> > > > for pt in range(0,nPts):
> > > >       minDist = 1000000
> > > >       pointFeature = pointsLayer.GetFeature(pt)
> > > >       for poly in range(0,nPolys):
> > > >             polyFeature = polysLayer.GetFeature(poly)
> > > >             Dist = pointFeature.GetGeometryRef().Distance(
> > > > polyFeature.GetGeometryRef() )
> > > >             if (Dist < minDist):
> > > >                   minDist = Dist
> > > >       print (pt,minDist)
> > > >
> > > > Thank you.
> > > >
> > > > Dave Verbyla
> > > >
> >
> > > _______________________________________________
> > > gdal-dev mailing list
> > > gdal-dev at lists.osgeo.org
> > > http://lists.osgeo.org/mailman/listinfo/gdal-dev
> >
> > --
> > Homme Zwaagstra
> > GeoData Institute
> > University of Southampton
> >
> > Tel: +44(0)2380 59 8709
> >

-- 
Homme Zwaagstra
GeoData Institute
University of Southampton

Tel: +44(0)2380 59 8709