Changing SQL syntax in QGIS Virtual Layers

Question

I am experiencing difficulties with SQL syntax in a Virtual Layer. I can do the simplest query form such as:

SELECT * FROM mytable

and this displays on my canvas.

However, if I try to name fields in my table such as:

SELECT field1, field2 FROM mytable

this doesn't create an error but does not display on my canvas.

Can anyone offer suggestions, please? I have tried it on several layers.

Are you getting something like? gis.stackexchange.com/questions/328990/… — GeorgeC
– GeorgeC, Commented Jul 17, 2019 at 4:47
If none of field1 or field2 is a geometry fields nothings will appear on the map canvas ... is that what u mean ? What kind of query do u intend to do ? — Snaileater
– Snaileater, Commented Jul 17, 2019 at 5:01

spatialthoughts · Accepted Answer · 2019-07-17 05:01:49Z

For virtual layers, the actual geometry of the features are in a column named geometry.

In your first query when you select all columns, you are implicitly selecting the geometry column. That's why you can see the features on the canvas.

In the second query, you are only selecting non-spatial columns (field1, field2 etc.) and they show up as a table. To fix that, update your query like below

SELECT field1, field2, geometry FROM mytable

Thank you for your help. I hadn't realised that a geometry field is required in the syntax. This solves my problem. Well done. — Colin Mazengarb
– Colin Mazengarb, Commented Jul 17, 2019 at 11:15

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