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<p>Hi Even
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<div class="moz-cite-prefix">On 02.09.2017 21:49, Even Rouault
wrote:<br>
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<blockquote type="cite" cite="mid:2310933.BSNKgXZh30@even-i700">
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<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;">There's a flow in your reproducer. You run OGR_DS_ExecuteSQL( ds, subsetQuery, NULL, NULL ); but do not use the resulting result layer. So basically this has no effect on the rest of your code (except a memory leak).</p>
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Ah yes indeed!<br>
<blockquote type="cite" cite="mid:2310933.BSNKgXZh30@even-i700">
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[...]
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<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;">The reason is that when issuing a SQL request there's no guarantee that it will result in a set of rows with unique identifiers (think of a join that could make several rows appear twice), so the FID on the result set of ExecuteSQL() are just a sequence starting at 0.</p>
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Ok makes sense. Though as far as QGIS goes, is there a case where a
subset query can result in duplicates?<br>
<blockquote type="cite" cite="mid:2310933.BSNKgXZh30@even-i700">
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<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;">If you know that your request will result in a result set with real FIDs you can use the following trick to get the FID column as a regular column (renaming the ogc_fid as something else, since there's special logic to ignre "ogc_fid as a regular field. If your FID field name is already something else than this default "ogc_fid", then you'll already get it as a regular field)</p>
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<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;">$ ogrinfo poly.sqlite -sql "select ogc_fid as this_is_the_fid, * from poly where ogc_fid = 10"</p>
<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;">INFO: Open of `poly.sqlite'</p>
<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;"> using driver `SQLite' successful.</p>
<p style="-qt-paragraph-type:empty; margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; "> </p>
<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;">Layer name: SELECT</p>
<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;">Geometry: Unknown (any)</p>
<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;">[...]</p>
<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;">Geometry Column = GEOMETRY</p>
<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;">this_is_the_fid: Integer (0.0)</p>
<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;">area: Real (0.0)</p>
<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;">eas_id: Integer64 (0.0)</p>
<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;">prfedea: String (0.0)</p>
<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;">OGRFeature(SELECT):0</p>
<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;"> this_is_the_fid (Integer) = 10</p>
<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;"> area (Real) = 5268.813</p>
<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;"> eas_id (Integer64) = 170</p>
<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;"> prfedea (String) = 35043413</p>
<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;"> POLYGON ((479750.6875 4764702.0,479658.59375 4764670.0,479640.09375 4764721.0,479735.90625 4764752.0,479750.6875 4764702.0))</p>
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</blockquote>
Something like this [1] seems to fix the issue, don't know if it's
the best way forward though?<br>
<br>
Thanks<br>
Sandro<br>
<br>
[1]
<a class="moz-txt-link-freetext" href="https://github.com/manisandro/QGIS/commit/e95eea6dfa3e7ce7d0c0796352fa39943be80031">https://github.com/manisandro/QGIS/commit/e95eea6dfa3e7ce7d0c0796352fa39943be80031</a><br>
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