AGGR using index fields - performance

[georgina_spary]

In an expression using AGGR, is it more performant to use a join field

=Sum(AGGR(ONLY([MyCount]), %%QV_RegnID))

or a non join field

=Sum(AGGR(ONLY([MyCount]), REGNID))

?

I know it's a bad idea to use join fields for display/ reporting but surely it's good to aggregate by an index? or is that not how QV works?

[marcus_sommer · Accepted solution]

Often it worked to calculate measures over KEY's but they could be have unexpected results. Therefore if it's possible you should avoid it and from a performance point of view aggr-functions could take a lot of ressources especially if they grab the data from many tables. Further see here: When should the Aggr() function NOT be used?.

- Marcus