topic Difference between autonumberhash128,autonumberhash256 and autonumber in QlikView

Difference between autonumberhash128,autonumberhash256 and autonumber

brindlogcool — Fri, 07 Dec 2012 15:55:56 GMT

Hi ,

What is the difference between autonumberhash128,autonumberhash256 and autonumber functions?

As per the help it is given the same definition for all the three functions.

This function can be used e.g. for creating a compact memory representation of a complex key.

Please share your inputs.

Re: Difference between autonumberhash128,autonumberhash256 and autonumber

Gysbert_Wassenaar — Fri, 07 Dec 2012 20:29:00 GMT

Autonumber needs one expression as input and autonumberhashXXX can handle more inputs. So you'd use autonumber(Field1&Field2&Field3) which needs to calculate the concatenation of Field1,-2 and -3 first. Autonumberhash can take more inputs: autonumberhash128(Field1, Field2, Field3). More importantly the autonumberhash are likely more efficient in determining if the combined inputs have already been encountered or are encountered for the first time. So they are probably faster in calculating the unique integer.

Re: Difference between autonumberhash128,autonumberhash256 and autonumber

schurter — Mon, 27 Mar 2017 12:43:48 GMT

Dear Gysbert,

Thanks for the statement - but what's then the difference between AutoNumberHash128 and AutoNumberHash256

Best, Marlies

Re: Difference between autonumberhash128,autonumberhash256 and autonumber

swuehl — Mon, 27 Mar 2017 13:32:10 GMT

Marlies,

the hash function maps data of arbitrary size to data of fixed size.

The difference between Hash128 and Hash256 is just the fixed size of the output range values, i.e. Hash256 allows more distinct values to map to, fewer collisions (input mapped to same output value).

But it will also consume more memory to store the hash values (but since these values are then Autonumber'ed, it doesn't really matter).

Re: Difference between autonumberhash128,autonumberhash256 and autonumber

schurter — Mon, 27 Mar 2017 13:39:56 GMT

Stefan, OK, thank for the answer!

Best, Marlies