QGIS show WKT from attribute table

Question

I have a dataset (from mysql) which I can load into QGIS. One of the columns in the table (and thus in the attribute table) is a WKT column. I am not able to select this column for the geometry.

The WKT looks like this: LINESTRING Z (101438.727 426681.927 -0.555, 101428.442 426687.427 -0.539). What I would like to do is to tell the vector layer to show all line strings based on the WKT in the attribute table.

All I can find was how to get geometries inside the attribute table, but I would like to do it the other way around.

I tried to create a geometry column, but that returns only NULL in my attribute table (and I still don't know how to tell QGIS to look in the attribute table of a geometry object)

What I use:

 geom_from_wkt(  "WKT" )

example below shows <geometrie: LineStringZ> but the attribute table shows NULL.

EDIT

I have a mysql table containing multiple columns and one of them is a WKT column. When I load the table using layer - add layer - vector layer I choose Database and create my connection.

At the moment a new layer is created with my whole mysql table as attribute table, and the layer has no geometry.

I would like to "tell" QGIS that the information regarding the geometry is inside the attribute table, in the column WKT (that is also the name of the column). What I would like to do is to display my spatial information (from mysql) inside QGIS.

The reason I am using text instead of mysql geometries is because the mysql geometries do not support 3D information (like LINESTRING Z).

Answer 1

If it's just for visualization you could use the geometry generator with the same expression:

geom_from_wkt("WKT")

To set it up you may duplicate your layer (so you will get one layer with the original geometry and the copy with the geometry from the WKT) or add a new symbol layer to display both geometry in original layer. Then in the Layer styling panel use the below setting (Symbol layer type : Geometry Generator ; Geometry type : Point/Multipoint):

Alternatively you can use the processing tool "Geometry by expression" (using again the same expression) but this will create a new layer so change on the original layer wont be reflected in this.

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EDIT : If you have no geometry in the original layer the best solution is to create a virtual layer based on your table where your SQL query generate the geometry from the WKT column, this way you get a layer that will stay synchronized with the original data.

You may adapt this to get the layer (replace : "Field &" , ... , "Field n" by the name of the field you want to get and mysql_TABLE by the name of your table)

SQL query :

SELECT "Field &" , ... , "Field n" , st_geomfromtext( "WKT") as geometry FROM mysql_TABLE