Spatial Query for a Virtual Layer

Question

I would like to use SQL to create a virtual layer in QGIS by clipping information from a large data set using a bounding box around my study area.

I have two questions. Is this an efficient way to work with large data sets (i.e., more efficient than just loading a large shapefile)?

How do I write the query? for it? I don't really know what I am doing, so far my query looks like this:

Select F* Where ST_Intersects(F.geometry,C.geometry)

At the moment, I keep crashing my computer with my queries. I will post back if I figure this out.

Answer 1

A sample syntax for you.

SELECT *
FROM F, C
WHERE st_within(F.geometry, C.geometry) = 1

On a side note:

• SELECT * will output everything (including geometry column) fits your conditions.
• FROM F,C will define the datasource
• WHERE is the condition, and st_intersects() requires 1 (TRUE) or 0 (FALSE). I chose st_within() for your case.

I hope testing this and comparing the speed with other methods answers your first question, too.