Generating dummy variable if point lies inside polygon using QGIS

The solution has been provided by @DPSSpatial already, but let me try to demonstrate a Virtual Layer approach (hence sqlite, as commented by DPSSpatial ):

Example

Please consider some elephants were observed in and out of the Singapore zoo. I would like to mark elephants "inside a green fence".

• Elephants: point layer -- loaded as csv through Delimited text layer.
• zoo: polygon layer (green) -- loaded as geojson file.

Virtual Layer

(1) Layer | Add Layer | Add/Edit Virtual Layer

(2) Import Elephants and zoo layers

(3) Give a query like below:

SELECT Elephants.*, st_within(Elephants.geometry, zoo.geometry) AS dummy
FROM Elephants, zoo
WHERE st_within(Elephants.geometry, zoo.geometry)

We will get something like:

Oh, sorry you wanted a complete list of [1, 0] in the dummy column... Then remove WHERE (filter) from the above query, i.e.:

SELECT Elephants.*, st_within(Elephants.geometry, zoo.geometry) AS dummy
FROM Elephants, zoo

You will obtain a full listing in the dummy column.