How can I 'pull' data from an MDX OLAP Cube into a standard SQL Server table?

问题

I've been provided access to a cube and need to know if I can set up a stored procedure that can connect to a Cube and retrieve the contents (via an MDX Query). I need this to prevent having to export the data from the Management Studio or from Excel (via PowerPivot). I'm very new to cubes/olap queries so forgive any naivety I may show.

回答1:

The easiest way is to create a linked server to your cube and then INSERT..SELECT FROM OPENQUERY http://sqlblog.com/blogs/stacia_misner/archive/2010/11/30/31193.aspx

This option has limitations in that

it has an 8000 character constraint on the MDX query
you must manually create a linked server for each database
special code is required to handle when result is empty
excessive data types in result set columns (ntext for columns and nvarchar(4000) for rows)

An advanced option is the ExecuteOLAP CLR stored procedure https://olapextensions.codeplex.com/

回答2:

If you choose to use OPENQUERY (easiest way, but having the limitations specified by Brian), the following procedure might be handy:

    /* 
PARAMS:
    @mdx: mdx statement
    @mdx_columns: specifies the mdx columns to retrieve from the executed mdx
    @linkedServer: linked server to be used
    @resultsTable: temporary table to hold results from mdx
    @resultsCols: if only some columns should be filled in @resultsTable, specify them here (e.g. '(col1, col2, ... )' )
    @expectedColCount: expected column count for mdx result. If actual column count is different from the expected count, no data is filled in
    @actualColCount: actual column count. Specify NULL if not interesed in this value
    @Debug: outputs debug info
*/
ALTER PROCEDURE [dbo].[exec_mdx_over_linked_server] (
    @mdx NVARCHAR(MAX),
    @mdx_columns NVARCHAR(1024) = '*',
    @linkedServer VARCHAR(64),
    @resultsTable VARCHAR(64),
    @resultsCols VARCHAR(1024) = '',
    @expectedColCount SMALLINT,
    @actualColCount SMALLINT = NULL OUTPUT,
    @Debug BIT = 0
)
AS
BEGIN
    SET NOCOUNT ON

    if (@Debug = 1)
        PRINT 'Started exec_mdx_over_linked_server procedure for populating ' + @resultsTable

    IF LEN(@MDX)>8000 RAISERROR ('MDX too long for openquery (exec_mdx_over_linked_server)', 
                                16,
                                1);

    declare @SQL NVARCHAR(MAX)

    IF (@Debug = 1)
    BEGIN
        -- getting results from mdx
        SET @SQL = 'SELECT ''Mdx results for ' + @resultsTable + ''' AS ''Mdx results'', ' + '*' + ' 
            FROM OPENQUERY(' + @linkedServer + ', ''' + @mdx + ''')';
        IF LEN(@SQL)>8000 RAISERROR ('MDX too long for openquery (exec_mdx_over_linked_server)', 
                                    16,
                                    1);
        EXEC (@SQL)
    END

    SET @SQL = '
        SELECT ' + '*' + ' INTO #resultsWithWeirdNameToAvoidTempCollisions
        FROM OPENQUERY(' + @linkedServer + ', ''' + @mdx + ''');

        SELECT @colCount = COUNT(*)
        FROM tempdb.sys.columns
        WHERE object_id = object_id(''tempdb..#resultsWithWeirdNameToAvoidTempCollisions'');

        if (@colCount = @expectedColCount)
            INSERT INTO ' + @resultsTable + @resultsCols + '
            SELECT ' + @mdx_columns +  ' FROM #resultsWithWeirdNameToAvoidTempCollisions'


    IF LEN(@SQL)>8000 RAISERROR ('MDX too long for openquery (exec_mdx_over_linked_server)', 
                                    16,
                                    1);

    if (@Debug = 1)
        PRINT 'dbo.exec_mdx_over_linked_server SQL = ' + @SQL

    DECLARE @colCount INT
    EXECUTE sp_executesql @SQL, N'@expectedColCount SMALLINT, @ColCount SMALLINT OUTPUT', @expectedColCount = @expectedColCount, @colCount = @actualColCount OUTPUT

    if (@Debug = 1)
    BEGIN
        PRINT '@expectedColCount = '; PRINT @expectedColCount
        PRINT '@actualColCount = '; PRINT @actualColCount
    END

    -- correction for small float numbers (< 10E-10)

    DECLARE @UpdateSql NVARCHAR(MAX) = N''
    DECLARE @SmallThreshold FLOAT = 0.00000000001


    SELECT @UpdateSql += '
                            UPDATE ' + @resultsTable + ' 
                            SET ' + QUOTENAME(COLUMN_NAME) + ' = 0 
                            WHERE TRY_CONVERT (FLOAT, ' + QUOTENAME(COLUMN_NAME) + ') IS NOT NULL
                                                 AND ABS(' + QUOTENAME(COLUMN_NAME) + ') < ' + CAST(@SmallThreshold AS NVARCHAR(30))
    FROM tempdb.INFORMATION_SCHEMA.COLUMNS with(NOLOCK)
    -- WHERE table_name like @resultsTable + '[_][_][_]%'
    -- changed, in order not to take into consideration objects from other spids
    WHERE table_name = object_name(object_id('tempdb..' + @resultsTable), (select database_id from sys.databases where name = 'tempdb'))

    IF (@Debug = 1)
    BEGIN
        PRINT '@UpdateSql = '; PRINT @UpdateSql;
    END

    EXEC (@UpdateSql);

END

It provides the following advantages:

handles the case when received result does not have the expected columns (nothing is performed)
performs some roundings for very small numbers (this might happen since the cube knows to work with floating point numbers only)
all mdx statements go through a single procedure

When profiling, I have noticed approx. 100ms overhead (execution through the procedure vs. direct execution against analysis server).

.NET developers can use ADOMD.NET framework, which allows running parameterized queries and having a smaller overhead.

来源：https://stackoverflow.com/questions/18984223/how-can-i-pull-data-from-an-mdx-olap-cube-into-a-standard-sql-server-table

标签

sql

sql-server

olap-cube