You can order the result set returned by relational SQL queries in Ascending, Descending, Selection Order or Default order. Default returns members based on the data source outline. Selection Order is the member selection order in Dimension Browser.
Unlike OLAP servers, relational cubes are compiled by Web Analysis Studio, and the label mode, alias tables, and selection order are manually coordinated. Sort by alias may perform comparatively slow, as the default query result set is sorted by ID. Sorting by alias requires a complete client-side re-sort.
The source of the relational dimension header sort impacts performance. Defining a relational dimension header sort using Data Layout, prompts Web Analysis Studio to sort all dimensions as part of the current query result set.
Alternatively, sorting a relational dimension using the data object shortcut menu (Data Display / Dimension Header Sort) requires you to select dimension headers.
Lastly, you can apply dimension header sort definitions to relational generations defined in the Generation Editor. These definitions only impact the Dimension Browser sort order. Using the Order By Mode drop-down list, you can also specify orders by ID or Alias.