SQL queries in shapefiles using python/gdal return none result

Question

I want try use Python and GDAL to create some SQL queries in my shapefiles. I try something and it looks good, but doesn't work. I get a none result.

Here is the code :

from osgeo import ogr
ogr_ds = ogr.Open('line.shp')
TEST=3
sql = "SELECT id FROM {} where id='{}'".format(ogr_ds,TEST)
layer = ogr_ds.ExecuteSQL(sql)
print layer

Answer 1

You are probably using the input layer in a wrong way; furthermore, also the .format{} operation doesn't seem correct.

You may try the following code:

from osgeo import ogr

filepath = 'C:/Users/path_to_the_shapefile/line.shp' # set the filepath
layer_name = filepath[:-4].split('/')[-1] # get the layer name
driver = ogr.GetDriverByName ("ESRI Shapefile")
ogr_ds = driver.Open(filepath)
TEST=3
sql = "SELECT id FROM %s WHERE id=%s" %(layer_name,TEST)
layer = ogr_ds.ExecuteSQL(sql)
print layer

I tested it with another shapefile (and a similar query) and it returns what expected:

print layer
<osgeo.ogr.Layer; proxy of <Swig Object of type 'OGRLayerShadow *' at 0x18A4D8F0> >

EDIT

If you want to print the id value, you may add these lines:

feat = layer.GetNextFeature()
val = feat.GetField(0)
print val

but this will only returns one feature and not all the queried features (this kind of operation would be useful if you are only interested in knowing if a specific value for the id field is stored in the input layer). Furthermore, you will get an error if there isn't any id value equals to the TEST variable.