Datamart DSL

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Introduction

MDX (MultiDimensional eXpressions)

MDX is a query language for OLAP databases, much like SQL is a query language for relational databases. It is also a calculation language, with syntax similar to spreadsheet formulas.

MDX has several elements that are used by, or influence, most statements:

  • Identifiers - Identifiers are the names of objects such as cubes, dimensions, members, and measures, e.g. [Time], [Measures].
  • Data Types - Define the types of data that are contained by cells, member properties, and cell properties. (details see Section #Data types )
  • Expressions (MDX) - An expression is a combination of identifiers, values, and operators. You can use an expression as part of the data to be retrieved by a query or as a search condition to look for data that meets a set of criteria. Expressions include functions that return a single value, a set expression, e.g. [Measures].[Discount Amount] * 1.5.
  • Operators - Operators are syntax elements that work with one or more simple MDX expressions to make more complex MDX expressions, e,g, +,-,*,/, <, >, AND, OR etc.
  • Functions - Functions are syntax elements that take zero, one, or more input values, and return a scalar value or an object, e.g. .Dimension, .Level , IsEmpty(),Order(), .CurrentMember etc.
  • Comments - Comments are pieces of text that are inserted into MDX statements or scripts to explain the purpose of the statement. MDX supports //, -- and /* ... */ as commenting characters.
  • Reserved Keywords - Reserved keywords are words that are reserved for the use of MDX and should not be used for object names used in MDX statements, e.g. SELECT, WHERE etc.

Data types

There are six primary data types in MDX:

Type Description
scalar Scalar is either a number or a string. It can be specified as a literal, e.g. number 5 or string "OLAP" or it can be returned by an MDX function, e.g. Aggregate(), .UniqueName , .Value etc.
Dimension /
Hierarchy		 Dimension is a dimension of a cube. A dimension is a primary organizer of measure and attribute information in a cube. MDX does not know of, nor does it assume any, dependencies between dimensions- they are assumed to be mutually independent. A dimension will contain some members organized in some hierarchy or hierarchies containing levels. It can be specified by its unique name, e.g. [Time] or it can be returned by an MDX function, e.g. .Dimension. Hierarchy is a dimension hierarchy of a cube. It can be specified by its unique name, e.g. [Time].[Fiscal] or it can be returned by an MDX function, e.g. .Hierarchy. Hierarchies are contained within dimensions.
Level Level is a level in a dimension hierarchy. It can be specified by its unique name, e.g. [Time].[Fiscal].[Month] or it can be returned by an MDX function, e.g. .Level.
Member Member is a member in a dimension hierarchy. It can be specified by its unique name, e.g. [Time].[Fiscal].[Month].[August 2014], by qualified name, e.g. [Time].[Calendar].[2014].[Q3].[August 2014] or returned by an MDX function, e.g. .PrevMember, .Parent, .FirstChild etc.
Note that all members are specific to a hierarchy. If the self-same product is a member of two different hierarchies ([Product].[ByManufacturer] and [Product].[ByCategory]), there will be two different members visible that may need to be coordinated in sets and tuples.
Tuple Tuple is an ordered collection of one or more members from different dimensions. Tuples can be specified by enumerating the members, e.g. ([Time].[Fiscal].[Month].[August], [Measures].[Sales]) or returned by an MDX function, e.g. .Item().
Set Set is an ordered collection of tuples with the same dimensionality, or hierarchality in the case of Microsoft's implementation. It can be specified enumerating the tuples, e.g. {([Measures].[Sales], [Time].[Fiscal].[2014]), ([Measures].[Sales], [Time].[Fiscal].[2014])} or returned by MDX function or operator, e.g. Crossjoin(), Filter(), Order(), Descendants() etc.
Other data types Member properties are equivalent to attributes in the data warehouse sense. They can be retrieved by name in a query through an axis PROPERTIES clause of a query. The scalar data value of a member property for some member can be accessed in an expression through MDX, either by naming the property (e.g., [Product].CurrentMember.[Sales Price]) or by using a special access function (e.g.,[Product].CurrentMember.Properties("Sales Price")). In limited contexts, MDX allows other data types as well - for example Array can be used inside the SetToArray() function to specify an array that is not processed by MDX but passed to a user-defined function in an ActiveX library. Objects of other data types are represented as scalar strings indicating the object names, such as measure group name in Microsoft's MeasureGroupMeasures() function or KPI(Key Performance Indicator) name in for example Microsoft's KPIValue() or KPIGoal() functions.

Basic Syntax of MDX query

► Syntax: 

-- One of the three ways to write comments
SELECT {set 0} on COLUMNS, /* block comment */
  {set 1} on ROWS // line comment
  ...
  {set n} on AXIS(n)
FROM [cube]
WHERE (tuple) // called "slicer dimension"

Note: Key differences between MDX and SQL

  • “Cube in, Cube out” for MDX.
  • set notation needs to be used after SELECT.
  • FROM clause can name only one cube
  • The WHERE clause describes the slicer axis (i.e., all the axes that is not a query axis) and is filtered by its default members


Examples

A typical query

► Example: 

SELECT {[Time].[Calendar].[Year].[2013], 
   [Time].[Calendar].[Year].[2014]} ON COLUMNS,
  {[Store].[Store Name].MEMBERS} ON ROWS
FROM [Sales]
WHERE ([Measures].[Store Sales])
.MEMBERS and .CHILDREN functions

► Syntax: 

Hierarchy.Members
Level.Members
...
Member.Children

Notes:

  • .Members returns the set of members in a dimension, level, or hierarchy.
  • .Children returns the set of children of a specified member.

► Example: 

SELECT {[Time].[Calendar].[Year].[2014].CHILDREN} ON COLUMNS,
  {[Store].[Store City].MEMBERS} ON ROWS
FROM [Sales]
WHERE ([Measures].[Store Sales])


Calculate Member

► Syntax: 

WITH MEMBER parent1.name1 AS ’expression1’
  MEMBER parent2.name2 AS ’expression2’

Notes:

  • If a calculated member is only required for a single MDX query, you can define that calculated member by using the “WITH” keyword. A calculated member that is created by using the “WITH” keyword no longer exists after the query has finished running.

► Example 1: 

WITH MEMBER [Time].[Calendar].[Year].[2014].[H1] AS
’[Time].[Calendar].[Year].[2014].[Q1] + [Time].[Calendar].[Year].[2014].[Q2]’
MEMBER [Time].[Calendar].[Year].[2014].[H2] AS
’[Time].[Calendar].[Year].[2014].[Q3] + [Time].[Calendar].[Year].[2014].[Q4]’
SELECT {[Time].[Calendar].[Year].[2014].[H1], 
   [Time].[Calendar].[Year].[2014].[H2]} ON COLUMNS
  [Store].[Store Name].MEMBERS ON ROWS
FROM [Sales]
WHERE ([Measures].[Profit])

► Example 2: define and use new measures 

WITH MEMBER [Measures].[ProfitPercent] AS
’([Measures].[Store Sales] – [Measures].[Store Cost]) / ([Measures].[Store Cost])’
SELECT [Time].[Calendar].[Year].[2014].CHILDREN ON COLUMNS,
 [Store].[Store Name].MEMBERS ON ROWS
FROM [Sales]
WHERE ([Measures].[ProfitPercent])
Slicer Dimension

► Example: Slice on the [Product] dimension 

SELECT {[Time].[Calendar].[Year].[2014].CHILDREN} ON COLUMNS,
  {[Store].[Store City].MEMBERS} ON ROWS
FROM [Sales]
WHERE ([Product].[Product Family].[Drink],
[Measures].[Store Sales])
Filter() function

► Syntax: 

FILTER(set, logical expression )

Notes:

  • Returns the set that results from filtering a specified set based on a search condition.

► Example: If we are only interested in stores whose 2014 unit sales exceed 1000 

SELECT {[Time].[Calendar].[Year].[2014].CHILDREN} ON COLUMNS,
   FILTER( {[Store].[Store City].MEMBERS},
           ([Measures].[Unit Sales], [Time].[Calendar].[Year].[2014]) > 1000 ) ON ROWS
FROM [Sales]
WHERE ([Measures].[Store Sales])
Order() function

► Syntax: 

ORDER(set, numeric/string expression, [, ASC | DESC | BASC | BDESC]

Notes:

  • Arranges members of a specified set, optionally preserving or breaking the hierarchy.

► Example 1: List all measures for each city in decreasing order of their sales count 

SELECT [Measures].MEMBERS ON COLUMNS,
    ORDER(
        [Store].[Store City].MEMBERS,
        [Measures].[Sales Count], 
        BDESC
    ) ON ROWS
FROM [Sales]


► Example 2: If we are only interested in stores whose name is between “Berlin” and “Heidelberg” 

SELECT [Measures].MEMBERS ON COLUMNS,
    ORDER(
        {[Store].[Store City].[Berlin]:[Heidelberg]},
        [Store].CURRENTMEMBER.Name,
        BASC
    ) ON ROWS
FROM [Sales]
Lag() function

► Syntax: 

Member.LAG(index)

Notes:

  • returns the member that is a specified number of positions before a specified member at the member's level.
  • .Lag(1) is equivalent to the .PrevMember function.
  • .Lag(-1) is equivalent to the .NextMember function.

► Example: list all measures for December 2014 

SELECT [Measures].MEMBERS ON COLUMNS,
       [Time].[Fiscal].[Month].[February 2015].LAG(2) ON ROWS
FROM [Sales]
Lead() function

► Syntax: 

Member.LEAD(index)

Notes:

  • returns the member that is a specified number of positions following a specified member at the member's level.
  • .Lead(n) is equivalent to .Lag(-n) function.

► Example: list all measures for December 2014 

SELECT  [Measures].MEMBERS ON COLUMNS,
        [Time].[Fiscal].[Month].[February 2015].LEAD(-2) ON ROWS
FROM [Sales]
PrevMember function

► Syntax: 

Member.PREVMEMBER

Notes:

  • the previous member in the level that contains a specified member.

► Example: list all measures for January 2014 

SELECT  [Measures].MEMBERS ON COLUMNS,
        [Time].[Fiscal].[Month].[February 2015].PREVMEMBER ON ROWS
FROM [Sales]


NextMember function

► Syntax: 

Member.NEXTMEMBER

Notes:

  • Returns the next member in the level that contains a specified member.

► Example: list all measures for March 2015 

SELECT  [Measures].MEMBERS ON COLUMNS,
        [Time].[Fiscal].[Month].[February 2015].NEXTMEMBER ON ROWS
FROM [Sales]
FirstChild function

► Syntax: 

Member.FIRSTCHILD

Notes:

  • Returns the first child of a specified member.
  • Leaf members have no children and therefore no first child.

► Example: list all measures for first quarter of 2015, which is the first child of year 2015 

SELECT  [Measures].MEMBERS ON COLUMNS,
        [Time].[Calendar].[Year].[2015].FIRSTCHILD ON ROWS
FROM [Sales]
LastChild function

► Syntax: 

Member.LASTCHILD

Notes:

  • Returns the last child of a specified member.
  •  Leaf members have no children and therefore no last child.

► Example: list all measures for march 2015, which is the last child of first quarter of year 2015 

SELECT  [Measures].MEMBERS ON COLUMNS,
        [Time].[Calendar].[Quarter].[Q1 2015].LASTCHILD ON ROWS
FROM [Sales]
Head() function

► Syntax: 

HEAD(set [ ,count ] )

Notes:

  • returns the first specified number of elements in a set.

► Example: show the profit of top-5 cities in terms of sales count 

SELECT [Measures].[Profit] ON COLUMNS,
    HEAD( ORDER( {[Store].[Store City].MEMBERS},
                [Measures].[Sales Count],
                BDESC 
               ), 
          5
        ) ON ROWS
FROM [Sales]


Tail() function

► Syntax: 

TAIL(set [ ,count ] )

Notes:

  • returns a subset from the end of a set.

► Example: show the profit of bottom-5 cities in terms of sales count 

SELECT [Measures].[Profit] ON COLUMNS,
    TAIL( ORDER( {[Store].[Store City].MEMBERS},
                [Measures].[Sales Count],
                BDESC 
               ), 
          5
        ) ON ROWS
FROM [Sales]
TopCount() function

► Syntax: 

TOPCOUNT(set, count [ ,numeric expression ] )

Notes:

  • Sorts a set in descending order and returns the specified number of elements with the highest values.
  • The numeric expression is used to evaluate the tuple values. If a numeric expression is not specified, the function returns the set of members in a natural order, without any sorting, behaving like Head() function.

► Example: show the profit of top-5 cities in terms of sales count 

SELECT [Measures].[Profit] ON COLUMNS,
    TOPCOUNT( [Store].[Store City].MEMBERS,
                5,
                [Measures].[Sales Count]
            ) ON ROWS
FROM [Sales]
BottomCount() function

► Syntax: 

BOTTOMCOUNT(set, count [ ,numeric expression ] )

Notes:

  • Sorts a set in ascending order, and returns the specified number of tuples in the specified set with the lowest values.
  • If a numeric expression is not specified, the function returns the set of members in a natural order, without any sorting, behaving like Tail() function.

► Example: show the profit of bottom-5 cities in terms of sales count 

SELECT [Measures].[Profit] ON COLUMNS,
    BOTTOMCOUNT( [Store].[Store City].MEMBERS,
                5,
                [Measures].[Sales Count]
            ) ON ROWS
FROM [Sales]
TopPercent() function

► Syntax: 

TOPPERCENT(set, percentage, numeric expression)

Notes:

  • Sorts a set in descending order, and returns a set of tuples with the highest values whose cumulative total is equal to or greater than a specified percentage.
  •  Percentage must be a positive value between 0 and 100.

► Example: show the best profit and cities that make the top 10% of sales count 

SELECT [Measures].[Profit] ON COLUMNS,
    TOPPERCENT( [Store].[Store City].MEMBERS,
                10,
                [Measures].[Sales Count]
            ) ON ROWS
FROM [Sales]


BottomPercent() function

► Syntax: 

BOTTOMPERCENT(set, percentage, numeric expression)

Notes:

  • Sorts a set in ascending order, and returns a set of tuples with the lowest values whose cumulative total is equal to or greater than a specified percentage.
  • Percentage must be a positive value between 0 and 100.

► Example: show the worst profit and cities that make the bottom 10% of sales count 

SELECT [Measures].[Profit] ON COLUMNS,
    BOTTOMPERCENT( [Store].[Store City].MEMBERS,
                    10,
                    [Measures].[Sales Count]
                 ) ON ROWS
FROM [Sales]


TopSum() function

► Syntax: 

TOPSUM(set, value, numeric expression)

Notes:

  • Sorts a set and returns the topmost elements whose cumulative total is at least a specified value.

► Example: show the smallest set of whose cumulative total using the profit measure is at least the sum of 50000, beginning with the members of this set with the largest number of sales count 

SELECT [Measures].[Profit] ON COLUMNS,
    TOPSUM ( [Store].[Store City].MEMBERS,
             50000,
             [Measures].[Sales Count]
           ) ON ROWS
FROM [Sales]


BottomSum() function

► Syntax: 

BOTTOMSUM(set, value, numeric expression)

Notes:

  • Sorts a set in ascending order and returns a set of tuples with the lowest values whose sum is equal to or less than a specified value.

► Example: Show the smallest set of whose cumulative total using the profit measure is at least the sum of 50000, beginning with the members of this set with the smallest number of sales count 

SELECT [Measures].[Profit] ON COLUMNS,
    BOTTOMSUM( [Store].[Store City].MEMBERS,
               50000,
               [Measures].[Sales Count]
             ) ON ROWS
FROM [Sales]


Aggregate() function

► Syntax: 

AGGREGATE(set [, numeric expression])

Notes:

  • Returns a number that is calculated by aggregating over the cells returned by the set expression.
  • If a numeric expression is not provided, this function aggregates each measure within the current query context by using the default aggregation operator that is specified for each measure.
  • If a numeric expression is provided, this function first evaluates, and then sums, the numeric expression for each cell in the specified set.

► Example: aggregate profit for all the calendar months 

WITH MEMBER [Time].[Calendar].[All sales] AS
    AGGREGATE([Time].[Calendar].[Month].MEMBERS, [Measures].[Amount])
SELECT [Time].[Calendar].[All sales] ON COLUMNS,
  [Store].[Store City].MEMBERS ON ROWS
FROM [Sales]
WHERE [Measures].[Profit]
Avg() function

► Syntax: 

AVG(set [, numeric expression])

Notes:

  • Evaluates a set and returns the average of the non-empty values of the cells in the set, averaged over the measures in the set or over a specified measure.

► Example: show the average profit for each calendar year 

WITH MEMBER [Measures].[Avg Profit] AS
      AVG( [Time].[Calendar].[Month].MEMBERS, Measures.[Profit])
SELECT
      Measures.[Avg Profit] ON COLUMNS,
      [Time].[Calendar].[Year].MEMBERS ON ROWS
FROM  [Sales]
Sum() function

► Syntax: 

SUM(set [, numeric expression])

Notes:

  • Show the sum of profit for all members of the [Product].[Category] hierarchy for calendar years 2013 and 2014

► Example: show the average profit for each calendar year 

WITH MEMBER [Measures].[Sum Profit] AS 
        SUM( { [Time].[Calendar].[Year].[2013],
               [Time].[Calendar].[Year].[2014] }
           , [Measures].[Profit]
           )
SELECT [Measures].[Sum Profit] ON COLUMNS,
         [Product].[Category].Members ON ROWS
FROM [Sales]
StdDev() function

► Syntax: 

STDDEV(set [, numeric expression])

Notes:

  • returns the sample standard deviation of a numeric expression evaluated over a set, using the unbiased population formula (dividing by n-1).

► Example: Show the standart deviation of profit, evaluated over the first 3 months of calendar years 2014, using the unbiased population formula 

WITH MEMBER [Measures].[Stddev Profit] AS 
	STDDEV( { [Time].[Calendar].[Month].[January 2014],
               [Time].[Calendar].[Month].[February 2014],
               [Time].[Calendar].[Month].[March 2014]}
           , [Measures].[Profit]
	   )


PeriodsToDate() function

► Syntax: 

PERIODSTODATE([level [, member]])

Notes:

  • returns a set of sibling members from the same level as a given member, starting with the first sibling and ending with the given member, as constrained by a specified level in the Time dimension.
  • If the member expression is missing, then the level hierarchy.CurrentMember will be used.
  • If level expression is missing, the parent level of the [Time].CurrentMember in the default time dimension of the cube will be used.

► Example: aggregate profit for first 8 calendar months of year 2014 

WITH MEMBER [Time].[Calendar].[first8Months2014] AS
    AGGREGATE (
        PERIODSTODATE(  [Time].[Calendar].[Year], 
                        [Time].[Calendar].[Month].[August 2014],
                     )
              )		
SELECT [Time].[Calendar].[All sales] ON COLUMNS,
    [Store].[Store City].MEMBERS ON ROWS
FROM [Sales]
WHERE [Measures].[Profit]


YTD() function

► Syntax: 

YTD([member])

Notes:

  • returns a set of sibling members from the same level as a given member, starting with the first sibling and ending with the given member, as constrained by the Year level in the Time dimension.
  • Ytd(member) is equivalent to PeriodsToDate(Year level, member).
  • if no member is defined, then [Time].currentMember is used.
  • this function will not work when the Type property is set to FiscalYears.

► Example: aggregate profit for first 8 calendar months of year 2014 

WITH MEMBER [Time].[Calendar].[first8Months2014] AS
    AGGREGATE (
                YTD( [Time].[Calendar].[Month].[August 2014] )
              )		
SELECT [Time].[Calendar].[All sales] ON COLUMNS,
    [Store].[Store City].MEMBERS ON ROWS
FROM [Sales]
WHERE [Measures].[Profit]


CROSSJOIN() function

► Syntax: 

CROSSJOIN(set1, set2)

Notes:

  • Returns the cross product of one or more sets.

► Example: the query axis (ROWS) is the combination of 2 cube dimensions 

SELECT [Time].[Calendar].[Year].[2014].CHILDREN ON COLUMNS,
    CROSSJOIN( [Store].[Store State].MEMBERS,
                [Product].[Product Family].MEMBERS
             ) ON ROWS
FROM [Sales]
WHERE ([Measures].[Profit])


NonEmpty() function

► Syntax: 

NONEMPTY(set1 [,set2])

Notes:

  • returns the set of tuples that are not empty from a specified set, based on the cross product of the specified set with a second set.

► Example: 

SELECT [Time].[Calendar].[Year].[2014].CHILDREN ON COLUMNS,
    NONEMPTY(
        CROSSJOIN( [Store].[Store State].MEMBERS,
                   [Product].[Product Family].MEMBERS
                 )
            ) ON ROWS
FROM [Sales]
WHERE ([Measures].[Profit])


NonEmptyCrossjoin() function

► Syntax: 

NONEMPTYCROSSJOIN(set1 [,set2, . . .][, count])

Notes:

  • returns a set that contains the cross product of one or more sets, excluding empty tuples and tuples without associated fact table data.
  • If count is not specified, the function cross joins all specified sets and excludes empty members from the resulting set.
  • If a number of sets is specified, the function cross joins the numbers of sets specified, starting with the first specified set.

► Example: 

SELECT [Time].[Calendar].[Year].[2014].CHILDREN ON COLUMNS,
    NONEMPTYCROSSJOIN( [Store].[Store State].MEMBERS,
                       [Product].[Product Family].MEMBERS
                     ) ON ROWS
FROM [Sales]
WHERE ([Measures].[Profit])

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Datamart DSL

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