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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US">Hello,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US">When doing a cross join (my_fishbones a, my_fishbones b), you multiply a by b, so 100K by 100K.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US">If your table has 3 records : 1, 2, 3, the cross join outputs : 1|1, 1|2, 1|3, 2|1, 2|2, 2|3, 3|1, 3|2, 3|3.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US">There are unnecessary crosses.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US">Add a condition : a.id > b.id to traverse only the half of the matrix.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US">Kind regards<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">De :</span></b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"> Bo Guo [mailto:bo.guo@gisticinc.com]
<br>
<b>Envoyé :</b> jeudi 5 février 2026 13:53<br>
<b>À :</b> PostGIS Users Discussion <postgis-users@lists.osgeo.org><br>
<b>Objet :</b> [ScanMail-Spam] Slowness in testing any crossing straight lines in a layer<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Hi There!<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">I have 100K straight lines in a layer - my_fishbone - with GIST indexed. However, the following SQL query did not finish within 20 minutes! Could you advise on any improvement ideas?<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">SELECT a.*, <a href="http://b.id">b.id</a><br>
FROM my_fishbones a, my_fishbones b<br>
WHERE a.geom && b.geom <br>
AND ST_Crosses(a.geom, b.geom)<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Thanks in advance!<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Bo Guo<o:p></o:p></p>
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