Additional column on Report Builder

When you are using Report Builder, an additional column may added automatically. This colunm is entity key of the data.

Grouping keys are definitely there by design. It is important to group on the keys to ensure consistency in results. This column are actually Base64 encoded smashed entity keys, basically your integer keys with a couple extra bits of information added, encoded as Base64 (in the case of composite keys, all the key column values are combined into this single string value). These should be used in your grouping expressions to ensure accurate grouping when other columns may overlap.