The autonumber() function in QlikView converts unique expression values passed to it into integer values by looking them up in an internal table. If a value is not found, it is added to the table and assigned the next integer. This allows non-integer fields to be used as efficient keys. The autonumberhash128() and autonumberhash256() functions work similarly but store hashed values of the expression rather than the full value. All three functions are useful for improving efficiency but their tables are cleared each time the script runs, so they cannot be used for keys in incremental loads.