MDX Data Manipulation - Retrieve Source Data Using DRILLTHROUGH
Applies to: 
SQL Server Analysis Services 
Azure Analysis Services
Fabric/Power BI Premium
Multidimensional Expressions (MDX) uses the DRILLTHROUGHstatement to retrieve a rowset from the source data for a cube cell.
In order to run a DRILLTHROUGH statement on a cube, a drillthrough action must be defined for that cube. To define a drillthrough action, in SQL Server Data Tools, in Cube Designer, on the Actions pane, on the toolbar, click New Drillthrough Action. In the new drillthrough action, specify the action name, target, condition, and the columns that are returned by a DRILLTHROUGH statement.
DRILLTHROUGH Statement Syntax
The DRILLTHROUGH statement uses the following syntax:
<drillthrough> ::= DRILLTHROUGH [<Max_Rows>] [<First_Rowset>] <MDX select> [<Return_Columns>]
< Max_Rows> ::= MAXROWS <positive number>
<First_Rowset> ::= FIRSTROWSET <positive number>
<Return_Columns> ::= RETURN <member or attribute> [, <member or attribute>]
The SELECT clause identifies the cube cell that contains the source data to be retrieved. This SELECT clause is the same to an ordinary MDX SELECT statement, except that in the SELECT clause only one member can be specified on each axis. If more than one member is specified on an axis, an error occurs.
The <Max_Rows> syntax specifies the maximum number of the rows in each returned rowset. If the OLE DB provider that is used to connect to the data source does not support DBPROP_MAXROWS, the <Max_Rows> setting is ignored.
The <First_Rowset> syntax identifies the partition whose rowset is returned first.
The <Return_Columns> syntax identifies the underlying database columns to be returned.
DRILLTHROUGH Statement Example
The following example demonstrates the use of the DRILLTHROUGH statement. In this example, the DRILLTHROUGH statement queries the leaves of the Store, Product, and Time dimensions along the Stores dimension (the slicer axis), and then returns the department measure group, department ID, and employee's first name.
DRILLTHROUGH
Select {Leaves(Store), Leaves(Product), Leaves(Time),*} on 0
From Stores
RETURN [Department MeasureGroup].[Department Id], [Employee].[First Name]