1. A computer program product comprising a machine-readable medium storing instructions that, when executed by at least one programmable processor, cause the at least one programmable processor to perform operations for improving distributed query processing in a database management system, the operations comprising: generating a result column, the generating comprising a plurality of worker jobs running in parallel to read tasks from a shared queue as part of a query plan operation, the query plan operation comprising a group-by column within an input set of input columns, the group-by column comprising an original dictionary for all values contained within the group-by column; creating a new dictionary for the result column, the new dictionary preserving a same ordering as the original dictionary; determining that the new dictionary has fewer entries than the original dictionary for the group-by column such that mapping is required between old value identifiers within the group-by column and new value identifiers within the result column; and renaming the old value identifiers to the new value identifiers using a mapping vector.