Database Dimensions - Configure the (All) Level for Attribute Hierarchies
Applies to: 
SQL Server Analysis Services 
Azure Analysis Services
Fabric/Power BI Premium
In Microsoft SQL Server SQL Server Analysis Services, the (All) level is an optional, system-generated level. It contains only one member whose value is the aggregation of the values of all members in the immediately subordinate level. This member is called the All member. It is a system-generated member that is not contained in the dimension table. Because the member in the (All) level is at the top of the hierarchy, the member's value is the consolidated aggregation of the values of all members in the hierarchy. The All member often serves as the default member of a hierarchy.
The presence of an (All) level in an attribute hierarchy depends on the IsAggregatable property setting for the attribute and the presence of an (All) level in a user-defined hierarchy depends on the IsAggregatable property of the attribute at the top-most level of user-defined hierarchy. If the IsAggregatable property is set to True, an (All) level will exist. A hierarchy has no (All) level if the IsAggregatable property is set to False.
Establishing the Topmost Level
If the IsAggregatable property is set to False on the source attribute of a level in a hierarchy, then no aggregatable level can appear in the hierarchy above that level. A non-aggregatable level must be the topmost level of any hierarchy or the IsAggregatable property of the source attributes for any levels above it must also be set to False.
All Member and (All) Level
The single member of the (All) level is called the All member. The AttributeAllMemberNameproperty on a dimension specifies the name of the All member for attributes in a dimension. The AllMemberName property on a hierarchy specifies the name of the All member for the hierarchy.