What do you call a virtual layer in SQL?
These layers are called virtual layers: they do not carry data by themselves and can be seen as views to other layers. Open the virtual layer creation dialog by clicking on Add Virtual Layer in the Layer menu or from the corresponding toolbar. The dialog allows you to specify an SQL query.
What do you mean by virtual layers in QGIS?
A special kind of vector layer allows you to define a layer as the result of an advanced query, using the SQL language on any number of other vector layers that QGIS is able to open. These layers are called virtual layers: they do not carry data by themselves and can be seen as views to other layers.
How to create a virtual layer in SQLite?
Functions from SQLite and spatial functions from Spatialite can also be used in a virtual layer query. For instance, creating a point layer out of a attribute-only layer can be done with a query similar to: SELECT id, MakePoint (x, y, 4326) as geometry FROM coordinates
When to use QGIS expressions in virtual layer?
Functions of QGIS expressionscan also be used in a virtual layer query. To refer the geometry column of a layer, use the name geometry. Contrary to a pure SQL query, all the fields of a virtual layer query must be named. Don’t forget to use the askeyword to name your columns if they are the result of a computation or function call.
Can a virtual layer ignore the geometry field?
No geometry: this option forces the virtual layer to ignore any geometry field. The resulting layer is an attribute-only layer. Geometry Column: this option allows to specify the name of the column that is to be used as the geometry of the layer.
When to use update SQL layer in PostGIS?
The Update SQL Layer option is available when you right click on a Layer in the Layers Panel, but only when the Layer Source is within a Spatial Database e.g. PostGIS. It allows the User to filter the source data by choosing the columns they wish to retrieve and by selecting only specific records using Structured Query Language (SQL).