The world of SQL Server - Mohit Nayyar

Conditional page breaks in SSRS are always something developer needs to work on in order to get it done. This is especially true when you need to render the same report in PDF.

Recently I need to implement the same and did that with a quick trick. Here is the sample SELECT I am using to demonstrate the same.

select 'Record 1' as record, 0 as PageBreak, 1 as grp
UNION ALL
select 'Record 2' as record, 0 as PageBreak, 1 as grp
UNION ALL
select 'Record 3' as record, 0 as PageBreak, 1 as grp
UNION ALL
select 'Record 4' as record, 1 as PageBreak, 2 as grp
UNION ALL
select 'Record 5' as record, 0 as PageBreak, 3 as grp
UNION ALL
select 'Record 6' as record, 0 as PageBreak, 3 as grp
UNION ALL
select 'Record 7' as record, 1 as PageBreak, 4 as grp
UNION ALL
select 'Record 8' as record, 0 as PageBreak, 5 as grp

 "Record" column is just to show unique records. The most important column here is "PageBreak", which is setting the conditional page break with "1". That means whenever there is "1" in "pagebreak" column you need a page break otherwise keep on displaying the records on same page. 

The other very important column is "grp". Well, you really don't need this column and still will be able to implement conditional page break functionality. But then SSRS will club all the records which requires page break into 1 grouping set, probably in the end with this sample data. So, in order to maintain the sequence of records we need to add a grouping column which will create a new group whenever it finds a different value in "pagebreak" column.

Now, lets move on to SSRS report. These steps will work in SSRS 2008. I am not adding standard steps of creating a data source and data set. I know you are all smart guys...

Simple enough, please follow these steps.

1. Add a table with 2 columns, record and pagebreak.
2. Now run the report and you will see all the records are coming in same page.
3. Next, add a parent group to this row, parent to "Details" group in "Row Groups". Please check "Image 1".
4. In the group expression select the "grp" column and the sorting, select "grp" in Sort by. Please check "Image 2".
5. MOST Important, select "Between each instance of a group" of the newly create group under "Page Break" tab. Please check "Image 3".

Yep, that's it, run the report now. And you will see 3 records on page 1, 1 record on page 2, 2 records on page 3 and 1 record on page 4 and page 5.

Image 1

Image 2

Image 3

There are also other ways of doing the same, but I find this one very easy to implement.

Don't forget to hide new group by just minimizing the width and you are good to go. Try to render the same in PDF, and it works like a charm....

- Mohit Nayyar

In some cases we need to generate the data based on a starting date, to an end data (today-getdate()). This process is called data extrapolation based on limited information (starting date). Here I am trying to achieve the same without storing data in temp./staging tables.

First I am creating a temp. table wih 2 rows for Demo and now I need to generate rest of the rows starting from given date to today's date.

Next step is to make use of CTE to generate sequence of rows and finally making use of CROSS JOIN to join the sequence with real data and get the desired output.

CREATE TABLE #TEMP (
  MYNAME    VARCHAR(10),
  STARTDATE DATETIME)

GO

INSERT INTO #TEMP
VALUES     ('Mohit',
            '2008-09-15')

INSERT INTO #TEMP
VALUES     ('Nayyar',
            '2008-09-22')

GO

WITH FIRST2(SEQ)
     AS (SELECT 1
         UNION ALL
         SELECT 1),
     FIRST4(SEQ)
     AS (SELECT 1
         FROM   FIRST2 X
                CROSS JOIN FIRST2 Y),
     FIRST16(SEQ)
     AS (SELECT 1
         FROM   FIRST4 X
                CROSS JOIN FIRST4 Y),
     FIRST256(SEQ)
     AS (SELECT 1
         FROM   FIRST16 X
                CROSS JOIN FIRST16 Y),
     FIRST65536(SEQ)
     AS (SELECT 1
         FROM   FIRST256 X
                CROSS JOIN FIRST256 Y),
     SEQROWS
     AS (SELECT ROW_NUMBER()
                  OVER(ORDER BY SEQ) AS SEQNUMBER
         FROM   FIRST65536 WITH (NOEXPAND))
        
SELECT   MYNAME,
         STARTDATE,
         DATEADD(DAY,N.SEQNUMBER - 1,STARTDATE)  AS EXTRAPOLATION
FROM     #TEMP
         CROSS JOIN SEQROWS N
WHERE    N.SEQNUMBER <= DATEDIFF(DAY,STARTDATE,GETDATE())
ORDER BY MYNAME,
         STARTDATE,
         3
GO

DROP TABLE #TEMP
GO  

- Mohit Nayyar

I recently found really useful information on temp. table and table variable usage. I am sure this will be useful to SQL Community as well.

http://www.sqlservercentral.com/articles/63472/

- Mohit 

While loading data in Fact tables we usually see a scenario where the fact data is available but there is no corresponding business key in the related dimension.

In this case we choose multiple options to resolve the issue.

1. Ignore that fact
2. Insert the associated business key in dimension table and return the newly generated surrogate key from dimension table. And now store the data in Fact table with the surrogate key.

The second approach relates to a term called “Inferred members”. All the other attributes of that dimension will also get updated in next run of dimension load (usually nightly load).

In SSIS there are multiple options available to implement the second case.

First approach is to do lookup on the dimension table and for all the rows that are now matching, insert the business key in Dimension table and then do the lookup again to get the surrogate key.

Second approach is to make use of Lookup and Script component. Lookup component will ignore rows with no matching business key in dimension table. Then script component will process only those rows where it didn’t find the associated surrogate key and finally insert the same in dimension table and return the associated surrogate key through stored procedure output parameter.

This script component approach is more efficient because its using the existing lookup component only once and then doing all the processing in script component.

But the additional benefit comes if we make use of .Net Generic.SortedDictionary class to store the cache information regarding the newly generated key. Read more about this here…
http://msdn.microsoft.com/en-us/library/f7fta44c(VS.80).aspx

- Mohit

Sometime its not feasible to process the full cube, so it makes sense to only process the selective measure group in the cube.

This is especially true when you have really big cube which takes time to process and sometime we just need to load data for only few business metrics.

Here is the small example to process only selective measure groups using “SSIS Analysis Services Processing Task”.

I am assuming that the measure group names are stored in a variable and after that we need to create “Processing Commands” to process the cube.

Processing Commands: We need to set this property in “Analysis Services Processing Task” to process the measure groups. So I will be using “Script Task” to generate the command.

Just make sure that the “Delay Validation” property of “Analysis Services Processing Task” is set to “True”.

Follow these steps now……..

1. Get comma separated list of all measure groups needs to be processed in local SSIS variable let say “varMeasureGroups”. You can get this list from some sort of configuration, so no hard-coding ;)
2. Creates the command using “Script Task” and store the final command in local SSIS variable let say “varCubeCommand”
3. In “Analysis Services Processing Task” task set the property “Processing Commands” using expressions to the recently created variable named “varCubeCommand”.
4. That’s it………no need to process the full cube now………

Recently I found this issue of deadlock variables in SSIS and finally made two solutions

1. Instead of declaring variables in Script properties (ReadOnlyVariables / ReadWriteVariables), better to make use of Dts.VariableDispenser.LockForRead / Dts.VariableDispenser.LockForWrite in the script to lock variables

2. I also solved my problem by running child packages out-of-proc (ExecuteOutOfProcess=TRUE in Execute Package Task), this is more to do with script caching.

But recently I saw something strange and found out that one of my script is making use of this type of code and I am getting this error again.....

    Dim var As Variables

    Dts.VariableDispenser.LockForWrite("User::VariableName")

    Dts.VariableDispenser.GetVariables(var)

      'Problem Line......Just remove the reference to Dts.Variables

      Dts.Variables("User::VariableName").Value = "Some Value"

      'Correct Line.......make use of locally declared "var" variable

      var("User::VariableName").Value = "Some Value"

   var.Unlock()

To solve the situation I made a quick fix and change my Dts.Variables to local variable collection I defined in the beginning "var".

As we can see in this script that we are locking one variable for write. But after using the GetVariables we MUST use "var" collection to write data and should NOT use Dts.Variables and that fixed my problem.

So I think this is some sort of double locking issue, like if I lock the variable using "Dts.VariableDispenser" and if I try to access the same variable again with Dts.Variables instead of "var" then SSIS tries to lock that again......

 - Mohit Nayyar

I just saw this new query tool from SQL Answers.

The beauty of this tool is to directly generate the output of any query into PDF / HTML / Excel / Word / CSV format. Please take a look here…....

http://www.sqlanswers.com/Software/SAQ/Default.aspx

This seems to be a lightweight tool to query multiple databases platforms like Microsoft SQL Server, Oracle, DB2, Microsoft Access and MySQL, but I just tested this for Microsoft SQL Server 2005 and I am really happy with this.

This makes things really easy when you need to send the output in PDF or HTML without any extra effort.

On the similar lines Microsoft also offers a “SQL Server Web Data Administrator” tool, which is very useful because of its basic web interface. You can find this here…….

http://www.microsoft.com/Downloads/details.aspx?familyid=C039A798-C57A-419E-ACBC-2A332CB7F959&displaylang=en

- Mohit Nayyar 

Today I saw a new product coming soon to do DTS to SSIS migration called DtsXchange

Looks promising and this is also capable to do something extra which built-in DTS migration doesn’t do like Dynamic Properties. Have a look here http://www.pragmaticworks.com/dtsxchange.htm

Users can also migrate existing DTS packages into SSIS using the migration wizard provided by SQL Server 2005 but this wizard doesn’t cover complete DTS package. So in some cases manual effort is required, and SSIS doesn’t support some of the DTS features, so the user has to manually implement the functionality in new SSIS package.

You can find some known issues in migration here http://technet.microsoft.com/en-us/library/ms143462.aspx

But on top of this SSIS allows you to run the existing DTS package even without any change, using a wrapper called “Execute DTS 2000 Package Task” in the new SSIS package.

So if you don’t have the bandwidth to migrate the existing package then keep on running the old DTS packages in SSIS and start making new packages in SSIS.

Obviously you will miss the “All NEW SSIS” but it’s an easy work around. But I think you will miss a lot, because SSIS is NOT a new name of DTS but it's a truly enterprise level ETL tool. So its always better to migrate to SSIS as soon as possible.

- Mohit Nayyar

At some point of time we all have to fine tune our old SQL Server queries or some of our colleague’s queries ;)

So I thought of writing something about common query performance problems and a checklist which can be used a make sure we didn’t miss anything.

- Mohit Nayyar

Recently I was proposing some of the high availability options for Microsoft SQL Server 2005, so thought of summarizing the same here....

SQL Server 2005 provides 4 basic options for high availability.

1.    SQL Clustering

2.    Database Mirroring

3.    Transactional Replication

4.    Log Shipping

Other than these 4 options some people also consider backup-restore and Database snapshots as other high availability options, which is really not true.....

"Database snapshots can be used as a recovery option from user/application specific errors or for reporting purposes when combined with other technologies. A snapshot is simply a read-only view of a database at a particular point in time, that’s why called - Database snapshots"

So let’s see all of them in more detail...

I will evaluate each high availability option on these parameters

Now lets take a closer look at the evaluating the different options…….

-       Mohit Nayyar