Mdx 2nddraft

MDX Language An Overview

Presented by:

Muhammad Saleh AL-Qurishi Fatooh AL-Qershi

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Agenda Introduction

Brief HistorySQL vs. MDX

MDX LanguageMDX syntaxNaming conventionsTuples and sets

How MDX is usedMDX queries

Using MDX for queriesSELECT, FROM, ON COLUMNS, ON ROWSWHERE

MDX expression References

MDX Solution Presentation By-Muhammad & Fatooh

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Introduction

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Brief History


When first conceived of by Panorama Software in the mid-1990s, MDX was an extension of SQL.

Its original name was Multi-Dimensional eXtensions, (says Mosha Pasumansky)

In less than a decade, the programming language MDX has become the de facto standard for reporting and analysis in business intelligence (BI) systems

It is supported by virtually every major vendor of BI servers, including Microsoft, SSAS, IBM, Hyperion, and SAP

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Why has MDX become so popular

The growth of the BI industry it self.Users need fast and intuitive access to company

information to make more profitable business decisions

It is uniquely able to navigate, query, and perform calculations against multidimensional structures


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How MDX Differs from SQL?SQL MDX

Designed to create, manage, and query relational databases in online transaction (OLTP) systems

Developed to navigate, query, and perform calculations in OLAP databases

Select, From, WhereSELECT <column 1>, <column 2>, <column n> FROM <table>

Select, From, WhereSELECT <axis specification> on columns, <axis specification> on rows FROM <cube>

WHERE clause is used to restrict (filter) the rows

WHERE clause points to a specific slice of an OLAP cube

Two dimensional result Multi-dimensional result

Select from relations Select from cubes

Rows in SQL are defined by the columns The columns do not define the rows and vice versa

Functions such as AVG, COUNT, MIN, MAX, SUM, STDEV, and VAR

Functions such as AVG, COUNT, MIN, MAX, SUM, STDEV, and VAR


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SQL Does Things that MDX Can’t

SQL is self-contained

•It is a data definition

language (DDL) for

•It is a data manipulation

language (DML)

MDX has almost no data

definition capabilities

•You can’t create an OLAP cube

using MDX

MDX and SQL work hand-in-

hand in BI applications,

each doing its part to support

self-service reporting and

analytics


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MDX Language


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What Is MDX? MDX is a language that

Expresses selections, calculations, and some metadata definitions against an Online Analytical Processing (OLAP) database

Provides some capabilities for specifying how query results are to be represented

Is not a full report-formatting languageThere are several different APIs that support MDX

OLE DB for OLAP, ADO MD, ADOMD.Net, XMLA


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MDX – Basic Terminology Cube – is a subset of data from the OLAP store, organized and

summarized into multidimensional structures Cell – One or more facts (measures) and dimension attributes that

represent one record in a cube Dimension – business factor used to group a fact record Hierarchy – Levels of aggregation in a dimension Level – Aggregation layer in a dimension hierarchy Member – value of a dimension attribute or a derived value from a

dimension attribute Measure – Fact. Numerical value that measures a business activity

and can be summarized MDX Solution Presentation By-Muhammad & Fatooh

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Naming Conventions


Working with the Store dimension shown in the diagram above, we’d indicate the Leominster member like this:

[Store].[All].[Massachusetts].[Leominster]

[Store].Leominster] with certain data and certain naming conventions

if we have a hierarchy of Time we can’t use [Time].[Oct] because we may have more than one October in different years. But we can use [Time].[June,2001] rather than [Time].[All].[2001].[Q2].[June]

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Tuples and SetsA tuple is a combination of members from different

dimensions Essentially a multidimensional member A single member is a simple tuple

([Time].[Jun, 2005]) simple tuple (one dimension) ([Customer].[Chicago, IL], [Time].[Jan, 2005]) tuple with two

dimensions Each member in the tuple has to be from a different

dimension E.g. tuple should not have two Time members

We can’t compose an empty tuple We can’t use syntax to compose a tuple from tuples


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Tuples and Sets(cont.)

A set is simply an ordered collection of tuples Sets are typically enclosed by curled "{ }" braces Specify the cells of a cube that are to be returned by the

query Often appear in the SELECT part of a query


SELECT{ ( [Time].[2005], [Measures].[Dollar Sales] ),( [Time].[Feb, 2005], [Measures].[Unit Sales] )}ON COLUMNS ,{ [Product].[Tools], [Product].[Toys] } ON ROWSFROM [Sales]

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Brackets, braces and the odd dot and comma


•Dimension and member names are enclosed within brackets [ ] especially if the name contains numbers,

spaces, other special characters or is a keywordBrackets[ ]

•To separate the dimension name from the member name. (to represent the hierarchy)•]Product[.]Drink[.]Beverages[Dots . – Separators

•Used to denote tuples•)]Product].[Drink].[Beverages[(Braces ( ) – Tuples

•Used to denote sets•Slide 6

Curly braces { } – Sets

•For range the constructionthe colon) : (

•To separate tuples in the setComma) ,(

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Question 1


Is the following a tuple or a set?([Time].[May], [Store].[Boston], [Product].[Anchovies])

Answer: ?

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Question 2 OK, now what about these two?

1- ([Store].[Boston], [Product].[Anchovies])

2- {([Time].[April], [Store].[Boston], [Product].[Anchovies]),

([Time].[May], [Store].[Boston], [Product].[Anchovies]),

([Time].[June], [Store].[Boston], [Product].[Anchovies]),

([Time].[July], [Store].[Boston], [Product].[Anchovies])}

Answer:?


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How MDX is used


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MDX Query SyntaxSELECT

{set defining the column headers}

ON COLUMNS,

{set defining the row headers}

ON ROWS

FROM [cube name]

WHERE [Slicer specification]


MDX is neither case-sensitive nor line-oriented

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MDX Query Syntax(cont.)

N Axes

0 Columns

1 Rows

2 Pages

3 Chapters

4 Sections


The phrase on axis(n) indicates that those members should be put on the axis numbered n.

A query that uses axis 1 must also use axis 0, and a query that uses axis 2 must also use axes 1 and 0

The SELECT keyword starts the clause that specifies what you want to retrieve

The ON keyword is used with an axis name to specify where dimensions from our database are displayed

If you desire more generic axis terms over the named terms, you can use the AXIS(index) naming convention

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Query example


SELECT{ [Measures].[Dollar Sales], [Measures].[Unit Sales] }ON columns,{ [Time].[Q1, 2005], [Time].[Q2, 2005] }ON rowsFROM [Sales]

Look at a grid of numbers that has the Massachusetts sales and costs for the first two quarters of 2005

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Slicer Clause (WHERE clause) WHERE clause is actually optional It is used to define the measure that is being

queried It can, and often does, extend to other dimensions

WHERE (Measures.[Sales Average], [Time].[Year].[1997])

It is not the same as filtering (such as SQL)Slicing does not affect selection of the axis members,

but rather the values that go into themFiltering reduces the number of axis members


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Five main execution stages after the query is successfully parsed:

1- Resolving the FROM clause

2- Resolving the WHERE clause

3- Resolving named sets in the WITH clause

4- Resolving the tuples on each axis

5- Calculating the cells brought back in the axis intersections

a. Resolving NON EMPTY intersections

b. (AS2005) Resolving the HAVING clause on each axis


The Execution Stages of a Query

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MDX Expression


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Calculated Member The core syntax for defining a calculated member on a

dimension is MEMBER MemberIdentifier AS ‘member-formula’ [,

properties...] The three main parts are:

Member identifier, which specifies the name, dimension and hierarchical positioning of the calculated member

Formula, which specifies how the calculated member’s results are derived

Optional properties, which can provide additional calculation, display, and other kinds of information


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Calculated Member(cont.)

Calculated Member in the WITH section of a query will not visible outside of the query.

If we use CREATE SET command, then it will be available to more than one query

We can drop it with the DROP SET command


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Calculated Member(WITH Section)


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Calculated Member(more than one dimension)


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Named Set The basic syntax for defining a named set that is

supported by most vendors is as follows:SET Set-Identifier AS ‘set-formula’

Named set in the WITH part of a query will not visible outside of the query.

If we use CREATE SET command, then it will be available to more than one query

We can drop it with the DROP SET command


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Named set using WITH clause


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Named set using CREAT SET


Analysis Services 2005

Essbase V9

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Common Functions


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.MEMBER The simplest form of an axis specification or

member selection involves taking the MEMBERS of the required dimensionReturns set of all members


SELECT Measures.MEMBERS ON COLUMNS,[Store].MEMBERS ON ROWSFROM [Sales]

SELECT Measures.MEMBERS ON COLUMNS,{[Store].[Store State].[CA], [Store].[Store State].[WA]} ON ROWSFROM [Sales]

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. CHILDREN Returns the set of all members of the level

immediately beneath the starting levelReturns the child members for a particular member

within the dimension


SELECT Measures.MEMBERS ON COLUMNS,{[Store].[Store State].[CA].CHILDREN,[Store].[Store State].[WA].CHILDREN} ON ROWSFROM [Sales]

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Both MEMBER & CHILDREN functions are used often in formulating expressions, but do not provide the ability to drill down to a lower level within the hierarchy


For this task, a function called DESCENDANTS is requiredThis function allows one to go to any level in depth

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Descendants()


The expression:Descendants( [Time].[1998],[Month])would return all twelve months 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 and 12 (that is, all the descendants of 1998 at the month level) And:Descendants( [Time].[1998].[Q2],[Month])would return all the descendants of Q2 at the month level, namely 4, 5 and 6

The syntax for the DESCENDANTS function is:DESCENDANTS(member, level [, flags])

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CrossJoin() CrossJoin() – cross-product of members or

tuples in two different sets Specify all possible combinations Syntax: CrossJoin (set1, set2)


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Filter() Reduce a set by including in the resulting set only those

elements that meet some criteria Arguments

Boolean Expression Set

Returns subset The syntax for Filter() is:

Filter (set, Boolean-expression) For example, the expression

Filter (

{ [Product].[Product Category].Members },

[Measures].[Dollar Sales] >= 500

)


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Order() To put the tuples in a set into a sequence based

on associated data values The syntax for the Order() function

Order (set1, expression [, ASC | DESC | BASC | BDESC])

Arguments Ordering criterion Set Flag option (ex. Ascending, descending)

Hierarchical order can be complex MDX Solution Presentation By-Muhammad & Fatooh

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Order() Example Given the set of product categories , we may want to sort them in

descending order by sales. A very simple query for this may look like the following;


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NON EMPTY Removing empty slices from query results Works on any axis, and with any dimensions and tuples


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NON EMPTY


Query with empty slices on rows Empty slices removed with NON EMPTY

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References MDX Solutions, Second Edition: With Microsoft® SQL Server™ Analysis Services

2005 and Hyperion® Essbase Fast Track to MDX by Mark Whitehorn, Robert Zare and Mosha Pasumansky MDX language reference http://msdn.microsoft.com/en-us/library/ms145506.aspx http://www.databasejournal.com/article.php/1459531


http://publib.boulder.ibm.com/infocenter/dzichelp/v2r2/topic/com.ibm.dwe.cubemdx.doc/mdx_concepts.html

http://msdn.microsoft.com/en-us/library/ms145506.aspx

http://www.databasejournal.com/article.php/1459531

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Thanks

? MDX Solution Presentation By-Muhammad & Fatooh

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