Microsoft SQL Server Analysis Services

MDX Functions for Time

Time functions in Multidimensional Expressions (MDX) are essential for analyzing data across different time periods, such as calculating year-to-date values, comparing periods, or identifying trends. These functions operate on time-related dimensions, typically a Date or Time dimension, allowing for sophisticated time-series analysis.

Understanding Time Dimensions

Effective use of time functions relies on a well-structured time dimension within your cube. This dimension should include hierarchies for different levels of granularity, such as Year, Quarter, Month, and Day. Common attributes include the name of the period, the start and end dates of the period, and potentially fiscal period information.

Key Time-Related MDX Functions

The following are some of the most commonly used MDX functions for time-series analysis:

• ParallelPeriod(Level_Expression [, Index [, Member_Expression]])

  Returns a member from the same relative position within a different period. Useful for comparing current period values to previous periods.

  SELECT
    [Measures].[Sales Amount] ON COLUMNS,
    [Date].[Calendar].[Month].MEMBERS *
    [Date].[Calendar].[Year].MEMBERS ON ROWS
  FROM [Adventure Works]
  WHERE
    (
      [Date].[Calendar].[Month].&[7] , -- July
      ParallelPeriod([Date].[Calendar].[Year], 1, [Date].[Calendar].[Year].&[2007]) -- Previous Year
    )

• OpeningPeriod([Level_Expression] [, Member_Expression])

  Returns the first member of a specified level, optionally within the context of a given member.

  SELECT
    [Measures].[Sales Amount] ON COLUMNS,
    [Date].[Calendar].[Year].MEMBERS ON ROWS
  FROM [Adventure Works]
  WHERE
    OpeningPeriod([Date].[Calendar].[Month], [Date].[Calendar].[Year].&[2007])

• ClosingPeriod([Level_Expression] [, Member_Expression])

  Returns the last member of a specified level, optionally within the context of a given member.

  SELECT
    [Measures].[Sales Amount] ON COLUMNS,
    [Date].[Calendar].[Year].MEMBERS ON ROWS
  FROM [Adventure Works]
  WHERE
    ClosingPeriod([Date].[Calendar].[Month], [Date].[Calendar].[Year].&[2007])

• LastChild(Member_Expression)

  Returns the last child of a specified member. Often used with hierarchies to get the last day of a month or the last month of a quarter.

  SELECT
    [Measures].[Sales Amount] ON COLUMNS,
    [Date].[Calendar].[Month].MEMBERS ON ROWS
  FROM [Adventure Works]
  WHERE
    LastChild([Date].[Calendar].[Year].&[2007].[Q1])

• YTD(Set_Expression)

  Returns a set of members from the beginning of the current period up to and including the current member. Requires a proper time hierarchy.

  WITH MEMBER Measures.[YTD Sales] AS
    YTD([Date].[Calendar].[Date].CurrentMember)
  SELECT
    [Measures].[YTD Sales] ON COLUMNS,
    [Date].[Calendar].[Date].MEMBERS ON ROWS
  FROM [Adventure Works]

• QTD(Set_Expression)

  Returns a set of members from the beginning of the current quarter up to and including the current member.

  WITH MEMBER Measures.[QTD Sales] AS
    QTD([Date].[Calendar].[Date].CurrentMember)
  SELECT
    [Measures].[QTD Sales] ON COLUMNS,
    [Date].[Calendar].[Date].MEMBERS ON ROWS
  FROM [Adventure Works]

• MTD(Set_Expression)

  Returns a set of members from the beginning of the current month up to and including the current member.

  WITH MEMBER Measures.[MTD Sales] AS
    MTD([Date].[Calendar].[Date].CurrentMember)
  SELECT
    [Measures].[MTD Sales] ON COLUMNS,
    [Date].[Calendar].[Date].MEMBERS ON ROWS
  FROM [Adventure Works]

• PeriodsToDate(Level_Expression [, Member_Expression])

  Returns a set of members from the beginning of the specified level up to and including the specified member. Similar to YTD/QTD/MTD but more general.

  SELECT
    [Measures].[Sales Amount] ON COLUMNS,
    [Date].[Calendar].[Day].MEMBERS ON ROWS
  FROM [Adventure Works]
  WHERE
    PeriodsToDate([Date].[Calendar].[Month], [Date].[Calendar].[Day].&[20070115])

• Ancestor(Member_Expression, Level_Expression)

  Returns the ancestor of a given member at a specified level. Crucial for navigating up the time hierarchy.

  SELECT
    [Measures].[Sales Amount] ON COLUMNS,
    [Date].[Calendar].[Month].MEMBERS ON ROWS
  FROM [Adventure Works]
  WHERE
    Ancestor([Date].[Calendar].[Day].&[20070115], [Date].[Calendar].[Month])

Best Practices for Time-Series Analysis

• Ensure your time dimension has a complete hierarchy.
• Use member unique names (MUNs) correctly when referring to specific dates or periods.
• Leverage calculated members to create recurring time-based measures like YTD, QTD, and MTD.
• Consider using date-related attributes in your time dimension (e.g., DayOfWeek, MonthName) for more descriptive filtering and slicing.
• Test your MDX queries thoroughly with representative data to ensure accuracy and performance.

Mastering these time functions will significantly enhance your ability to derive insights from temporal data within your SQL Server Analysis Services cubes.