QGIS/resources/context_help/QgsQueryBuilder

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<h3>Query Builder</h3>
The query builder allows you to create provider specific filter expressions.
These are usually evaluated much faster than the generic QGIS expressions, but
are sometimes limited (e.g. for shape files) or behave diffently.
<h4>Providers</h4>
<table border=1>
<tr>
<th>Provider</th>
<th>Documentation</th>
</tr>
<tr>
<td>OGR</td>
<td>where clauses depending on the
<a href="http://www.gdal.org/ogr/ogr_formats.html">format</a> (eg.
<a href="http://www.gdal.org/ogr/ogr_sql.html">OGR SQL</a>
for shape files)
</td>
</tr>
<tr>
<td>PostgreSQL/PostGIS</td>
<td>where clauses using
<a href="http://www.postgresql.org/docs/">PostgreSQL</a> and
<a href="http://postgis.net/documentation">PostGIS</a>
</td>
</tr>
<tr>
<td>SpatiaLite</td>
<td>where clauses using
<a href="http://www.sqlite.org/lang_select.html">SQLite</a> and
<a href="http://www.gaia-gis.it/gaia-sins/spatialite-sql-4.1.0.html">SpatiaLite</a>
</td>
</tr>
<tr>
<td>Oracle Spatial/Locator</td>
<td>where clauses using
<a href="http://docs.oracle.com/cd/B28359_01/appdev.111/b28400/sdo_index_query.htm#autoId9">Oracle Spatial/Locator</a>
</td>
</tr>
<tr>
<td colspan=2>...</td>
</tr>
</table>