I have a large feature dataset with thousands of entries. Each entry is represented by a polygon. The most have unique values in all fields but some of them have to be merged based on a identity number in a field (zip code). I want to merge these polygons without losing the other field values. Is there a operation for this in QGIS?
You can use
Menu Processing / Toolbox / Aggregate for this. See the documentation: https://docs.qgis.org/3.16/en/docs/user_manual/processing_algs/qgis/vectorgeometry.html#aggregate
To keep all attribute values, you can concatenate them. This works well for string (text) fields. If you have integers, you must convert them to string using
attribute with the name of the respective attribute). Don't forget to set the resulting field-type to text and define a field-length long enough to include all values: