Summarizing fields with same ID in QGIS Field Calculator

Question

I am looking for a command, that sums the value of the field "Baulast" if they have the same "ogc_fid" and if there is a Number in the field "WEA". If there is no number in the field "WEA" -> 'keine Baulast'. Maybe something like

if("WEA">NULL, sum("Baulast","ogc_fid"), 'keine Baulast')

So as seen on the Picture, I want to sum the fields that have same ogc_fid and have a number in "WEA".

Answer 1

As an alternative you may try this expression:

if("WEA" IS NOT NULL,
    array_sum(
        array_agg(
            "Baulast",
            group_by:="ogc_fid",
            filter:="WEA" IS NOT NULL
            )
        ),
    'keine Baulast'
    )

Answer 2

Why not simply:

sum(
    expression:="Baulast",
    group_by:="ogc_fid",
    filter:="WEA" is not NULL
)

See the docs: https://docs.qgis.org/testing/en/docs/user_manual/expressions/functions_list.html#sum

Combine it with if:

if(
    "WEA" is not NULL,
    to_string(sum( -- since the field is a string, dont forget to convert the sum result to a string
        expression:="Baulast",
        group_by:="ogc_fid",
        filter:="WEA" is not NULL,
    )),
    'Keine Baulast'
)