# Calculating distance from centroid points to multiple polygon edges with SpatialLite

My question builds on a question previously asked (Calculating all distances from single points to multiple polygons). User @alexandre-neto provided an answer that I've worked on, but it isn't giving me the result I need. I'm new to SpatialLite and using QGIS 3.6 on a Windows OS.

I've created a SpatialLite database that has a point and a polygon layer. The point layer is the centroid of a sampling grid and the polygon layer comes from a government database called the 'Vegetation Resource Inventory (VRI)', which includes lots of data on stand age, species composition, wetlands, etc...

I want to create a new layer or a table of distances from the centroid of my sampling grid (Named: `"Grid Pothole Center"`) to the nearest edge of the VRI polygon layer (Named: `"Pothole VRI")`. It looks like SpatialLite offers a way to do this. I used the following code from instructions on the link provided above:

``````SELECT
f.id,
g.id,
st_distance(f.geom, st_centroid(g.geom)) AS distance

FROM
'Grid Pothole Center' AS f,
'Pothole VRI' AS g
``````

Note: `'Grid Pothole Center'` and `'Pothole VRI'` have a common field called `'id'`. This runs from the SpatiaLite DB manager plugin (select the database and ran the SQL statement above) without any error messages and a result is given. However, I get an empty table x with the following headings: `id, id:1, distance` - but no data in the table. What have I done wrong here?

Notice that your SQL is actually wrong because by the SQL standard `SELECT … FROM 'Grid Pothole Center'` means "select from string `Grid Pothole Center`" The table name should be enclosed between double quotation marks, but SQLite is lenient and really accepts also single quotes in this case. Still, take a habit to use double quotes in the future.
• Thank you for explanations, especially using `"double quotes"` May 28, 2019 at 4:25