Direct Query: Relationship vs Merge

[wlknsnBI]

Hi,

I would like to know the difference in terms of performance between relationships and merge when using direct query. Especially for 1-1 tables. When I load a visual in which I have merged certain fields in advance (basically folding it into a sql query), is there a difference in the query plan using this approach vs when I simply have the two tables in the model and set a relationship between them and add that related field?

With this I also wonder: what part of the query gets executed on load of the visual: is is the folded query and whatever it needs on the visuals (so adding relationships and calculations to the query), or always just what the visual needs regardless of what was set in terms of merges etc?
=> so for instance, if you merged two tables in advance, but the related merged field is not in the visual, does it get queried?

Thanks in advance

[lbendlin]

I would recommend you make extensive use of the Performance Analyzer and of DAX Studio.  The Performance Analyzer will give you the exact query (or queries) that the visual produces, and DAX Studio lets you look at the Query plans in excruciating detail.

A visual will only ever fetch the columns it needs to render, never any other columns.