field calculator - Expression string builder QGIS

I created a virtual field in my layer where I want a specific value to be calculated. In my attribute table I have several columns. The expression I am trying to create is the following. I want to iterate through all features and add all values of the column age who have a specific value, let's say the name of the features should be marc. In my first attempt I created this:

CASE WHEN  "name"  = "marc" THEN  sum(  "age" ) END

But it kinda doesn't work and I don't know how to iterate though all features in the layer and only choose those features with the name marc. Any advice?

Answer

You could use something like the following:

sum( "age", "name", "name" = 'marc' )

---

Where:

• "age" is the field used to calculate the sum;


• "name" is the field used to group the different names together;


• "name" = 'marc' is the expression used to filter all names in the name field which equal marc.