Tuesday 27 March 2012

SQL Server # Storing Hierarchical Data – Parent Child n’th level # TSQL

Introduction

Today, I would like to explain one way in which we can store the HIERARCHICAL data in SQL tables. A general table structure which people come up to store this kind of data is -

1

Where, EmployeeID id the UniqueID alloted to every new employee record inserted into the table and ManagerID is the EmployeeID of the immediate manager of the employee. Keeping in mind that Manager is also an employee.

Problem Statement

This table structure very well serves the purpose as long as we have 1-Level hierarchy. However, if the hierarchy is of n'th level, the SELECT statement to fetch the records becomes more complex with this kind of table structure. Suppose, we want to fetch the complete TREE of a particular employee, i.e. list of all the employees who are directly or indirectly managed by a particular employee. How to do it……..?

Thanks to CTE’s for making the life a bit easier – as using them in a recursive manner, we can get the work done. Please follow this msdn link to see an implementation using recursive CTE.

Suggested Table Structure

2

Here, I have just included a new column [PATH]. It is of VARCHAR(MAX) type. I have taken it as VARCHAR(MAX) just to make sure the field is long enough to store the complete path. But one can assign appropriate size as per their system’s requirement.

The basic idea of the [path] column is to store the complete hierarchical path of any employee separated by a delimiter as under -

3

Calculating the new path is very simple. It’s just, {New Path} = {Parent Path} + {Self ID} + {Delimiter}

Now, suppose if I want to fetch all the employees who are directly or indirectly working under EmployeeID = 2, I can use the below tsql -

;WITH CTE AS (
SELECT 1 EmployeeID,NULL ManagerID, '\1\' [Path]
UNION ALL    
SELECT 2 EmployeeID,1 ManagerID, '\1\2\' [Path]
UNION ALL    
SELECT 3 EmployeeID,1 ManagerID, '\1\3\' [Path]
UNION ALL    
SELECT 4 EmployeeID,2 ManagerID, '\1\2\4\' [Path]
UNION ALL    
SELECT 5 EmployeeID,4 ManagerID, '\1\2\4\5\' [Path]
)
SELECT
  *
FROM
  CTE
WHERE
  [Path] LIKE '%\2\%'

We can use a simple logic to even find out the level of the Employee -


SELECT
  *,
  (LEN([Path]) - LEN(REPLACE([Path],'\',''))) - 2 [Level]
FROM
  CTE
WHERE
  [Path] LIKE '%\2\%'

4

2 is subtracted from the formula as the length of delimiter for Level-0 is 2.

Conclusion

Hope, this simple trick could save a lot of time for the ones who find themselves lost playing with the hierarchical data.

Monday 12 March 2012

Last Execution Date Time of a Stored Procedure

On many forums I have found a very basic yet important query - “How can I know when was my Stored Procedure last executed?” And today through this blog I will try to answer this question.
Actually speaking, without explicit logging or tracing, it is not possible to get this information for each and every Stored Procedure of our Database. However, we can get this detail along with many other relevant information for the stored procedure having it’s execution plan currently cached on the server by using - sys.dm_exec_procedure_stats It’s a system dynamic view that returns aggregate performance statistics for cached stored procedures. Please note that this view has been introduced from SQL Server 2008.
The important thing to note is that this view returns one row for each cached stored procedure plan, and the lifetime of the row is as long as the stored procedure remains cached. When a stored procedure is removed from the cache, the corresponding row is eliminated from this view.
So, let’s see a way, using which at least we can find out the some important facts for the cached stored procedures -
USE DBName
GO
 
SELECT 
  O.name,
  PS.last_execution_time
FROM 
  sys.dm_exec_procedure_stats PS 
INNER JOIN sys.objects O 
  ON O.[object_id] = PS.[object_id] 

P.S. Please replace the DBName with the actual name of the Database.

The above script will return the name of all the cached stored procedure of the current database with their last execution time.

For more details on this dynamics view, please refer - sys.dm_exec_procedure_stats (Transact-SQL)

Friday 9 March 2012

Moving MASTER Database

In my previous post we see how to move MSDB database, today we will see how to move or relocate MASTER database. While moving MASTER database we’ll have to consider few other things like changing start-up parameter for SQL Server Service. I will also mention those stops here for better understanding. Let’s do it step-by-step.

Step 1: Query sys view and note down the existing location for MASTER database


USE MASTER
GO
SELECT
NAME,
PHYSICAL_NAME AS 'PhysicalFilePath',
STATE_DESC AS 'DB Status'
FROM SYS.MASTER_FILES
WHERE NAME LIKE 'Mast%'

Screen001

Step 2: Run alter database command and change the location for database files


ALTER DATABASE MASTER
MODIFY FILE
(
NAME = MASTER,
FILENAME= 'C:\SQLDB\Demo\Master.mdf'
)
GO
ALTER DATABASE MASTER
MODIFY FILE
(
NAME = MastLog,
FILENAME= 'C:\SQLDB\Demo\MastLog.mdf'
)
GO

Screen002

Step 3: Stop SQL Server Service and move database files to new location


Step 4: Restart SQL Server Service, surprised ?


Screen003 


Step 5: This was expected, let’s see what errorlog has to say about this!


Screen004


Refer the highlighted section, SQL Server service could not find the files. This is because we have moved that files to new location.


Step 6: Okay, so let’s go and change the start-up parameter. We can do this using Configuration manager.


Step 7: Right click on SQL Server service –> Properties –> Start-up Parameter


Screen005


Step 8: Make correction in path for Master.mdf and Master.ldf


Step 9: Start SQL Server service, this time it will start.


You are done!!


Note: This is to be done when we have to do relocate databases to new drive, or file organization, or some error which force us to do this.


-- Hemantgiri S. Goswami

Wednesday 7 March 2012

Moving MSDB to new location

In recent past we have a situation where in we required to move MSDB, Model and Master databases to new location, the reason being faulty drive. While moving system databases to new location we need to be extra cautious. Let’s see the process step-by-step.
Step 1: Let’s query sys view and note down the location for database files

SELECT
NAME,
PHYSICAL_NAME AS 'PhysicalFilePath',
STATE_DESC AS 'DB Status'
FROM SYS.MASTER_FILES
Screen001
Step 2: Run alter database and specify new location for database
SELECT
ALTER DATABASE MSDB
MODIFY FILE
(
NAME = MSDBData,
FILENAME= 'C:\SQLDB\Demo\MSDBData.mdf'
)
GO
ALTER DATABASE MSDB
MODIFY FILE
(
NAME = MSDBLog,
FILENAME= 'C:\SQLDB\Demo\MSDBLog.mdf'
)
GO
Screen002
Step 3: Stop SQL Server service
Screen003
Step 4: Once SQL Server service is stopped move MSDB database to new location
Step 5: Now, start SQL Server service. This time it will use the new path that we have configured in Step 2.
Note: If you have enabled and configure Database Mail, please make sure it works after you moved MSDB to new location.

Tomorrow, I will post about how to relocate Master database.

-- Hemantgiri S. Goswami (http://www.sql-server-citation.com/)

Tuesday 6 March 2012

Register for SQL Server 2012 Virtual Launch

`As we all are aware SQL Server 2012 virtual launch is scheduled after 60 hours roughly. Earlier I have discussed what’s new in SQL Server 2012 setup, MS has released SQL Server 2012 training kit and made it available for us to download. In recent past, I have blogged about a free eBook for SQL Server 2012 written by Ross Mistry ( Blog | Twitter ) and Stacia Misner ( Blog | Twitter) .

You will see lots of new and insightful information on new and enhanced features introduced in SQL Server 2012, this includes:

  • AlwaysOn
  • Automating AlwaysOn management
  • New backup and restore capabilities
  • ColumnStore index
  • Semantic Search
  • User-defined server roles
  • Data quality service
  • StreamInsight for SQL Server 2012
  • Big data analytics and Hadoop
  • T-SQL Enhancements
  • SQL Server Data Tools (SSDT)
  • SQL Azure
    Sounds interesting ?
    Get yourself register for the event, you will find the agenda of the event here.