[Gdal-dev] Another Question about OGRDataSource::ExecuteSQL

[Frank Warmerdam]

jody at ifi.unizh.ch wrote:
> Hi
> 
> I assume that the SQL statement passed to ExecuteSQL
> refers to the attributes of the features in the Datasource.
> 
> If the DataSource contains only one layer,
> everything seems to  be well-defined, because
> all features within a layer must have the same sorts of attributes.
> 
> But what happens if the datasource contains more than one layer
> (which it can, corresponding to the explanation in ogr_arch.html)
> which have different attribute schemas?
> 
> Or does an additional restriction apply to features in a
> "multilayered" Datasource?

Jody,

You specify the layer name as the table name in the OGR "pseudo-SQL".

For instance "SELECT eas_id, prop_value FROM polylayer" would return a
row/feature for each feature in the layer "polylayer", and include only
the eas_id and prop_val attributes.

Have you read the OGR SQL document?

   http://www.remotesensing.org/gdal/ogr/ogr_sql.html

Best regards,

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