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Posts Tagged ‘SQL Server 2012’

SQL SERVER – How to get total row count from OFFSET / FETCH NEXT (Paging)

Posted in Solutions, SQL SERVER, tagged , , , , , on March 30, 2015| Leave a Comment »

Paging became quite simpler & easy to script and manage by using OFFSET & FETCH NEXT keywords in SQL Server 2012 & above. I have written quite a detailed article earlier about it and implemented it in my most of the solutions wherever required. However, when you implement/use paging in your script, you face a big challenge, that is, to find the total number of records in that particular result-set.

Given below are the three methods which you can use to get the total row count from OFFSET / FETCH NEXT.
Before proceeding with the solutions, let me create a sample.

Sample : 

USE AdventureWorks2014
GO
-- Create Sample Table Table
CREATE TABLE [dbo].[SalesOrderDetail](
[SalesOrderID] [int] NOT NULL,
[SalesOrderDetailID] [int] NOT NULL,
[CarrierTrackingNumber] [nvarchar](25) NULL,
[OrderQty] [smallint] NOT NULL,
[ProductID] [int] NOT NULL,
[SpecialOfferID] [int] NOT NULL,
[UnitPrice] [money] NOT NULL,
[UnitPriceDiscount] [money] NOT NULL,
[LineTotal] [numeric](38, 6) NOT NULL,
[rowguid] [uniqueidentifier] NOT NULL,
[ModifiedDate] [datetime] NOT NULL
) ON [PRIMARY]
GO

-- Insert bulk data into sample table
-- It may take few minutes depends upon the server performance
INSERT INTO [dbo].[SalesOrderDetail]
SELECT * FROM [SALES].[SalesOrderDetail]
GO 100

-- Verfiy the data
Select * from [dbo].[SalesOrderDetail]
GO

Method 1 : Using COUNT(*) OVER()

USE AdventureWorks2014
GO
DECLARE
@PageSize INT = 10,
@PageNum  INT = 1;

SELECT
[SalesOrderID]
, [SalesOrderDetailID]
, [CarrierTrackingNumber]
, [OrderQty]
, [ProductID]
, [SpecialOfferID]
, [TotalCount]= COUNT(*) OVER()
FROM [dbo].[SalesOrderDetail]
ORDER BY SalesOrderID
OFFSET (@PageNum-1)*@PageSize ROWS
FETCH NEXT @PageSize ROWS ONLY;
GO
--OUTPUT

row count using Offset 1.1

Method 2 : Using Common Table Expression

USE AdventureWorks2014
GO
DECLARE
@PageSize INT = 10,
@PageNum  INT = 1;

;WITH Main_CTE AS(
SELECT [SalesOrderID]
, [SalesOrderDetailID]
, [CarrierTrackingNumber]
, [OrderQty]
, [ProductID]
, [SpecialOfferID]
FROM [dbo].[SalesOrderDetail]
)
, Count_CTE AS (
SELECT COUNT(*) AS [TotalCount]
FROM Main_CTE
)
SELECT *
FROM Main_CTE, Count_CTE
ORDER BY Main_CTE.SalesOrderID
OFFSET (@PageNum-1)*@PageSize ROWS
FETCH NEXT @PageSize ROWS ONLY
GO
--OUTPUT

row count using Offset 1.1

Method 3 : Using Cross Apply

USE AdventureWorks2014
GO
DECLARE @PageSize INT = 10,
@PageNum  INT = 1;

SELECT
[SalesOrderID]
, [SalesOrderDetailID]
, [CarrierTrackingNumber]
, [OrderQty]
, [ProductID]
, [SpecialOfferID]
, [TotalCount]
FROM [dbo].[SalesOrderDetail]

CROSS APPLY (SELECT COUNT(*) TotalCount
FROM [dbo].[SalesOrderDetail] ) [Count]
ORDER BY SalesOrderID
OFFSET (@PageNum-1)*@PageSize ROWS
FETCH NEXT @PageSize ROWS ONLY
GO
--OUTPUT

row count using Offset 1.1

All of the above methods give you the same result-sets. Lets view their performance given below.

S.No

 Method

CPU Time

Elapsed Time

1

 COUNT(*) OVER()

30654 ms

40372 ms

2

 Common Table Expression

11762 ms

7665 ms

3

 Cross Apply

11794 ms

7373 ms

Conclusion :
On the basis of above results, I would recommend that you either use Common Table Expression or Cross Apply to get the faster results.

Note : The above queries have been tested on ~12 Million records.

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SQL SERVER – How to convert yyyymm to Mon-yyyy

Posted in Solutions, SQL SERVER, tagged , , , , , on July 14, 2014| 1 Comment »

Recently, I was developing a report for one of my customers, who migrated their database from SQL Server 2005 to SQL Server 2012 Enterprise Edition. The database belongs to a legacy system , so I found couple of conversion issues, however the major issue I faced in developing the report was the date format. The required date format was Mon-yyyy and the data available in the table was in the format of yyyymm.

Before proceeding with the solution, let me create a sample to demonstrate the problem.

USE tempdb
GO
DROP TABLE tbl_Sample
GO
CREATE TABLE tbl_Sample
(
[ID] INT,
[Date] varchar(6)
)
GO
INSERT INTO tbl_Sample VALUES (1,'201401')
INSERT INTO tbl_Sample VALUES (2,'201402')
INSERT INTO tbl_Sample VALUES (3,'201403')
INSERT INTO tbl_Sample VALUES (4,'201404')
INSERT INTO tbl_Sample VALUES (5,'201405')
INSERT INTO tbl_Sample VALUES (6,'201406')
INSERT INTO tbl_Sample VALUES (7,'201407')
INSERT INTO tbl_Sample VALUES (8,'201408')
INSERT INTO tbl_Sample VALUES (9,'201409')
INSERT INTO tbl_Sample VALUES (10,'201410')
INSERT INTO tbl_Sample VALUES (11,'201411')
INSERT INTO tbl_Sample VALUES (12,'201412')
GO
SELECT * FROM tbl_Sample
GO

Convert YYYYmm 1.1

Solution 1 : Traditional Method
This is the old traditional method, which is compatible with SQL Server 2005 and above. In this method, you need to use many functions (LEFT, DATENAME, CONVERT, YEAR) to convert yyyymm date format to Mon-yyyy. Given below is the script.

USE tempdb
GO
SELECT
LEFT(DATENAME(MM,CONVERT(DATE,[Date]+'01')),3)
+ '-'
+ CONVERT(VARCHAR(4),YEAR(CONVERT(DATE,[Date]+'01'))) As [Mon-Year]
FROM tbl_Sample
GO

Convert YYYYmm 1.2

Solution 2 : New Method
This is the new method, which is compatible with SQL Server 2012 and above. In this script, I will use a newly shipped (in SQL Server 2012) function namely Format to reduce the line of script in order to convert yyyymm to Mon-yyyy. Given below is the script.

USE tempdb
GO
SELECT FORMAT(CONVERT(DATE,[Date]+'01'),'MMM-yyyy') As [Mon-Year]
FROM tbl_Sample
GO

Convert YYYYmm 1.2

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SQL SERVER – How to convert Select statement result set into Insert statements

Posted in Solutions, SQL SERVER, tagged , , , , , on July 11, 2014| Leave a Comment »

Conversion of Select statement result set into Insert statement is a very frequent activity that a DBA/Developer needs to create, mostly when they need to migrate small amount of data from one instance to another or from one environment to another. I recently created one of my customer’s new branch database from other branches database and came across this scenario. Fortunately, we do have a solution since SQL Server 2005 but it was very complicated specially when you need to do it for the tables as they have numerous columns. The reason I am writing this solution is that you can do it in few clicks in SQL Server 2012 and above.
Before proceeding with the solution, I would like to create a sample to demonstrate the solution.

Sample :
Given below is a select statement in which I modified the result set to demonstrate.

USE [AdventureWorks2012]
GO
SELECT [DepartmentID]
,[Name] + ' Department' As [Name]
,[GroupName]
,Getdate() As [ModifiedDate]
FROM [HumanResources].[Department]
GO

Convert select.1.1

Given below are the two solutions, one of them is traditional solution and another one you can use it in SQL Server 2012 and above.

Solution 1 : Using String concatenation (Traditional Method)
In this solution, you need to concatenate the result set of the Select statement in order to convert into Insert statement (with some modifications in the data). You need to make sure that single quotes(‘) are in proper locations. In addition, if the data in the result set does not belong to string data type you must convert into string data type to concatenate. In case, the table is having identity column, you must pass the column name in the INSERT STATEMENT as well with SET IDENTITY_INSERT. The reason why I DO NOT recommend this solution is because if you have more number of columns in the table, it takes more time for the development and debug as well.

USE [AdventureWorks2012]
GO
SELECT
'INSERT INTO tbl_sample (
[DepartmentID],[Name],[GroupName],[ModifiedDate])
VALUES(' + CONVERT(VARCHAR(50),[DepartmentID])
+ ',''' + [Name] + ' Department'' ,'
+ ''''+ [GroupName] + ''','
+ ''''+ CONVERT(VARCHAR(50),GETDATE(),120) + ''')'
FROM [HumanResources].[Department]
GO

Convert select.1.2

Solution 2 : Using Generate Script (New Method)
This method is applicable to SQL Server 2012 and above and you will find it quite simple. Let me explain this method using two simple steps.

Step 1 :
First of all, you need to develop a select statement like I did it in the sample based on your requirements and INSERT INTO A TABLE as shown below.

USE [AdventureWorks2012]
GO
SELECT [DepartmentID]
,[Name] + ' Department' As [Name]
,[GroupName]
,Getdate() As [ModifiedDate]
INTO [tbl_Department_Sample]  -- Result set inserted in a table
FROM [HumanResources].[Department]
GO

Convert select.1.3

Step 2 :
Your select statement result set has been inserted into the table([tbl_Department_Sample]). Now, you just need to generate the script (data only) of the table ([tbl_Department_Sample]) using Generate Script feature in SQL Server 2012 and above.

Let me know if you come across these scenarios and their solutions.

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SQL SERVER 2012 – Fix – Error :22939 – The parameter @supports_net_changes is set to 1.

Posted in Errors, SQL SERVER, tagged , , , , , on July 6, 2014| Leave a Comment »

Change Data Capture (CDC) is one of the frequently used features in SQL Server 2008 and above, it records any (CDC enabled) table’s changes and stores in audit tables. Recently, I upgraded one of my client’s database from SQL Server 2005 database to SQL Server 2012 and one of the key reasons to upgrade is to utilize the new features in the upgraded version. Once I started enabling CDC feature in few tables of the database it gave me given below error.

Message Number: 22939

Severity : 16

Error Message: The parameter @supports_net_changes is set to 1, but the source table does not have a primary key defined and no alternate unique index has been specified.

Error Generation:
I presume that CDC has been enabled on this particular database. Let me create a sample table to demonstrate this error.

USE AdventureWorks2012
GO
--Create Sample Table
CREATE TABLE tbl_Sample
(
[ID] INT NOT NULL,
[NAME] VARCHAR(50)
)
GO

-- Enable CDC feature on this table with net changes support parameter.
USE AdventureWorks2012
GO
EXEC sys.sp_cdc_enable_table
@source_schema = N'dbo',
@source_name = N'tbl_sample',
@role_name = NULL,
@supports_net_changes = 1
GO
--OUTPUT

Error Message 22939.1

Msg 22939, Level 16, State 1, Procedure sp_cdc_enable_table_internal, Line 194
The parameter @supports_net_changes is set to 1, but the source table does not have a primary key defined and no alternate unique index has been specified.

Ooopps…… I am NOT able to enable CDC on sample table.

Resolution:
The reason behind this error is that you do not have either primary key or unique index on the sample table and you want to enable net changes support in CDC. Before proceeding with the resolution, you should check whether you can create a Primary Key or Unique Index on the table to avoid such error.
Given below is the simple script to add Primary Key OR Unique Index in the sample table.

--Create Primary Key
USE AdventureWorks2012
GO
ALTER TABLE dbo.tbl_Sample ADD PRIMARY KEY (ID)
GO

-- Create Unique Index
USE AdventureWorks2012
GO
ALTER TABLE tbl_Sample
ADD CONSTRAINT UX_Constraint UNIQUE (ID)
GO
--OUTPUT

You can execute any one of the above scripts and can create Primary Key or Unique Index in the sample table.

Once you executed the above script, you can easily enabled the CDC with supports_net_changes as shown below.

USE AdventureWorks2012
GO
EXEC sys.sp_cdc_enable_table
@source_schema = N'dbo',
@source_name = N'tbl_sample',
@role_name = NULL,
@supports_net_changes = 1
GO
--OUTPUT

Command(s) completed successfully.

Error Message 22939.2

Conclusion :
Remember, whenever you need to enable CDC with supports_net_changes, make sure that the particular table HAS either Primary Key or Unique Index in order to avoid this error.

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SQL SERVER – How to delete recent connection from Connect to Server window in SSMS

Posted in Solutions, SQL SERVER, tagged , , , , , , on June 29, 2014| 1 Comment »

How to delete recent connection from Connect to Server window in SSMS is a very common issue and it becomes frustrated if you connect many servers on daily basis and SQL Server Management Studio (SSMS) pile up all the new server names in the list of Connect to Server window as shown below.

list of connection.1.1

I have been facing this common problem since SQL Server 2005 and it has been reported on Connect as well. Fortunately we do have a solution explained in this article that demonstrate step by step how to delete the recent connection list using mru.dat and SqlStudio.bin in SQL Server 2005  and SQL Server 2008 respectively. However, this is NOT smart solutions because it deletes all your recent connections including the active ones as well.

In SQL Server 2012, a proper solution came in the picture and I believe, this is much better than the earlier solution. Let me demonstrate it step by step.

Step 1 :
In order to open “Connect to Server” window, first of all you need to select file menu and click on connect object explorer.. in SSMS as shown below.

list of connection.1.3

Step 2 :
Once you open the Connect to Server window, you will find all recent connections in the server name as shown below but the drawback is you cannot determine what belongs to SQL Authentication and what to Windows.

list of connection.1.1

Step 3 :
Now, you need to eliminate the connection. In order to do it, you need to select the particular connection and press DELETE button from the keyboard. Once you press delete button, it will delete that particular connection but it will remain as selected in the server name dropdown list as shown below. If you need to delete multiple connections, you need to select server one by one and press delete button to delete  it,  as multiple selection is NOT allowed.

list of connection.1.2

Let me know if you come across this scenario and how did you resolve it.

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SQL SERVER – How to create a Sub Directory in FileTable using TSQL

Posted in Solutions, SQL SERVER, tagged , , , , , on May 30, 2014| 2 Comments »

In my earlier article, I have explained that creating a directory / sub directory in any file table is same like creating a directory / sub directory in windows itself. However, sometimes you need to create these directories and sub directories via T-SQL. I came across a case recently where I had to create a series of sub directories inside a directly using T-SQL.

Prerequisite :
I strongly recommend that you read the given below articles to have a clear understanding about FileTables.

  1. FileTables – Prerequisites
  2. FileTables – Data Definition Language (DDL)
  3. FileTables – Data Manipulation Language (DML)

Let me explain the solution step by step.

Step 1 :
First of all you need to create a sequence (A new object shipped with SQL Server 2012) to generate a series of IDs. However you can use any other techniques to create these series.

--This script is compatible with SQL Server 2012 and above.
--DROP SEQUENCE [dbo].[NewID]
--GO
CREATE SEQUENCE [dbo].[NewID]
AS [bigint]
START WITH 100000000
INCREMENT BY 1
CACHE
GO

Step 2 :
In this step, you need to create the given below procedure that can generate a new ID for your sub directory. Remember that filetable maintains directory and sub directory IDs in a hierarchy ID datatype. So you must get the parent folder ID (directory hierarchy ID) in order to create a child folder (sub directory). You can get further detail about hierarchy ID here. This stored procedure is self explanatory.

--This script is compatible with SQL Server 2012 and above.
--DROP PROCEDURE dbo.GetNewPathLocator
--GO
CREATE PROCEDURE dbo.GetNewPathLocator
@MainFolderID HIERARCHYID,
@SubDirectoryPath VARCHAR(MAX) OUTPUT

AS
BEGIN

DECLARE @FirstSeqNum sql_variant,
@LastSeqNum  sql_variant

EXEC sys.sp_sequence_get_range
@sequence_name = N'dbo.NewID'
, @range_size = 3
, @range_first_value = @FirstSeqNum OUTPUT
, @range_last_value = @LastSeqNum OUTPUT

SELECT @SubDirectoryPath = CONCAT(COALESCE(@MainFolderID.ToString(),'/'),
CONVERT(VARCHAR(20),@FirstSeqNum) ,'.',
CONVERT(VARCHAR(20),Convert(BIGINT,@FirstSeqNum)+1) ,'.',
CONVERT(VARCHAR(20),@LastSeqNum) ,'/')

END
GO

Step 3 :
Now, it is time to create a sub directory in any directory using T-SQL. I already created a directory inside a filetable as shown below.

creating sub directory in filetable

Let us create a sub directory inside that directory.

--This script is compatible with SQL Server 2012 and above.
DECLARE @MainFolderPath AS HIERARCHYID
--You must have the given below file table (dbo.DataBank)
--and directory (IT) inside file table in the existing database.
SELECT @MainFolderPath=path_locator FROM dbo.DataBank
WHERE [name]='IT'

DECLARE @SubDirectoryPath varchar(max)
EXEC dbo.GetNewPathLocator
@MainFolderID=@MainFolderPath
, @SubDirectoryPath = @SubDirectoryPath OUTPUT

--SELECT @SubDirectoryPath

INSERT INTO dbo.DataBank (name,path_locator,is_directory,is_archive)
VALUES ('sub directory', @SubDirectoryPath, 1, 0);
GO

Given below is the new sub directory created inside IT folder via T-SQL.

creating sub directory in filetable 2

Conclusion :
Remember, filetable keeps directory and sub directory IDs in Hierarchy ID datatype. So you must go through this concept. In addition, the whole process is self explanatory.

Let me know if you came across this situation and how you handled it.

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SQL SERVER – Working with Change Data Capture – Part 4

Posted in Audit, SQL SERVER, tagged , , , , , , on May 5, 2014| 1 Comment »

In my earlier articles, I discussed & demonstrated all basic activities in Change Data Capture (CDC) in any SQL Server database. However, I did not discuss about the retention period of CDC data in the database. In most cases, we need to modify the retention period due to our business requirements. I came across this query many times, if we can modify retention period, if Yes, how ?

BY DEFAULT, CDC configure the data retention period of 3 days. In other words, CDC keeps all the data changes history for 3 days ONLY and the rest will be cleaned (deleted). In most of my clients, I configured CDC for few tables with the retention period of 10 days and few of them leave it as a default (3 days).

Let me explain how to view / modify the retention period of CDC from in few easy steps.

Step 1 – View the existing RETENTION period in CDC:
First of all, you should check the existing retention period of CDC. It is also important to know that CDC keeps the retention period in minutes. Given below script will show the retention period in minutes as well as days by using dbo.cdc_jobs (a change data capture system table).

--This script is compatible with SQL Server 2008 and above.
USE msdb
GO
SELECT [retention] As [Retention period in minutes]
,[retention]/60/24 As [Retention period in days]
FROM
dbo.cdc_jobs
WHERE job_type ='cleanup'
GO
--OUTPUT

Change data capture.4.4_part1

Step 2 – Modify the RETENTION period in CDC :
As you can see in the above result that the retention period is 3 days (4320 minutes). Lets modify it to 10 days by using sys.sp_cdc_change_job (a system stored procedure of CDC).

--This script is compatible with SQL Server 2008 and above.
USE AdventureWorks2012
GO
DECLARE @New_retention_period_in_minutes AS SMALLINT
DECLARE @New_retention_period_in_days AS TINYINT

--Set the retention period for 10 days
SET @New_retention_period_in_days = 10

--Convert 10 days into minutes
SET @New_retention_period_in_minutes= @New_retention_period_in_days*60*24

--Select the total number of minutes in 10 days to check.
SELECT @New_retention_period_in_minutes
As [Retention period in minutes]

--Update minutes in the CDC job
EXECUTE sys.sp_cdc_change_job
@job_type = N'cleanup',
@retention = @New_retention_period_in_minutes;
GO
--OUTPUT

Change data capture.4.4_part2

Step 3 – Verify the RETENTION period in CDC:
You need to execute the same script as Step 1 but the output would be different this time, as we have successfully updated the retention period to 10 days in Step 2.

--This script is compatible with SQL Server 2008 and above.
USE msdb
GO
SELECT [retention] As [Retention period in minutes]
,[retention]/60/24 As [Retention period in days]
FROM
dbo.cdc_jobs
WHERE job_type ='cleanup'
GO
--OUTPUT

Change data capture.4.4_part33

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SQL SERVER – Working with Change Data Capture – Part 3

Posted in Audit, SQL SERVER, tagged , , , , , , , on May 4, 2014| 1 Comment »

In my earlier two articles, I demonstrated how to enable and utilize the Change Data Capture (CDC) in any SQL Server database with few simple steps. However if you enable this feature for testing purpose in the test server, or sometimes you enable it on the wrong database / table  by mistake, so you need to disable it by following few steps as shown below. Before proceeding with the disability of CDC feature in the database, you must make sure that you DO NOT need the changes recorded by CDC because once you disable it, the CDC data will no longer be available.

Let me explain how to disable the CDC from any respective table & database in few easy steps.

Step 1 – Validating SQL Server Agent:
First of all you must make sure that your SQL Server Agent is UP and RUNNING as shown below.

Change data capture.3.1_part3

Step 2 – Find capture instance name :
The next step is to find the name of the capture instance (audit table) of any particular table that you need to disable for CDC. In order to achieve it, you need to execute sys.sp_cdc_help_change_data_capture (system stored procedure) to get all the list of CDC enabled objects along with its capture instance name as shown below.

Please note, if you need to disable CDC for database ONLY kindly skip this step.

--This script is compatible with SQL Server 2008 and above.
USE AdventureWorks2012
GO
sys.sp_cdc_help_change_data_capture
GO
--OUTPUT

Change data capture.3.2_part3

Step 3 – Disable CDC for tables:
Once you have the list, you need to note the capture instance name and execute the given below script with schema, table & capture instance name.
This script will disable the CDC feature for the particular table and you will lose all the CDC data for the given below table.

Please note, if you need to disable CDC for database ONLY kindly skip this step.

--This script is compatible with SQL Server 2008 and above.
USE AdventureWorks2012
GO

EXEC sys.sp_cdc_disable_table
@source_schema = N'HumanResources',
@source_name   = N'Department',
@capture_instance = N'HumanResources_Department'
GO
--OUTPUT

Change data capture.3.3_part3

Step 4 – Disable CDC for database:
In this step, we will disable the CDC feature from any database. Given below is the script that will NOT only disable CDC for any database but also will disable the CDC for all tables in that database. So be careful while executing this statement.

--This script is compatible with SQL Server 2008 and above.

USE AdventureWorks2012
GO

EXEC sys.sp_cdc_disable_db
GO
--OUTPUT

Change data capture.3.4_part3

Let me know if you enabled CDC in your SQL Server and its feedback.

An update of my blog is available at my twitter or you can like my Facebook page or subscribe via email by mentioning your email address in the ‘follow blog’ section.

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SQL SERVER – Working with Change Data Capture – Part 2

Posted in Audit, SQL SERVER, tagged , , , , on April 29, 2014| 1 Comment »

In my earlier article, I have explained how to enable Change Data Capture (CDC) features for any database and its tables in few easy steps. It seems to me that it is very simple and straight forward activity. Just few lines of codes can give you a kick start. The next step is to avail the benefits of CDC, when you perform a series of DML (Data Manipulation Language) statements and CDC records, it automatically?? without a single line of code.

Let me execute INSERT / UPDATE / DELETE statements against the particular tables, which we have enabled for CDC in the earlier article to demonstrate how CDC works.

Please NOTE that before proceeding with CDC you MUST make sure that your SQL SERVER AGENT IS UP AND RUNNING.

  • Impact of INSERT STATEMENT in CDC:

Let me pass an INSERT statement and observe how CDC records its changes in the audit tables as shown below.

--This script is compatible with SQL Server 2008 and above.
USE [AdventureWorks2012]
GO
--Insert a record in [HumanResources].[Department]
INSERT INTO [HumanResources].[Department]
([Name]
,[GroupName]
,[ModifiedDate])
VALUES
('IT'
,'R & D'
,GETDATE())
GO

Once you insert a new record in the table ([HumanResources].[Department]), lets review the table ([HumanResources].[Department]) and its relevant audit table (cdc.HumanResources_Department_CT) respectively.

--This script is compatible with SQL Server 2008 and above.
USE AdventureWorks2012
GO
SELECT * FROM HumanResources.Department
GO
SELECT * FROM cdc.HumanResources_Department_CT
GO
--OUTPUT

Change data capture.2.1_part2

As you can observe from the above result set, it has one new record in [HumanResources].[Department] as usual. In addition, one record has been inserted in the audit table (cdc.HumanResources_Department_CT) as well with some additional fields and ONE of the most important additional fields is _$operation that will explain you which operation inserted this record in the audit table. In the above result set say, _$operation has a value of 2 and it means that it has been inserted by INSERT statement.

  • Impact of UPDATE STATEMENT in CDC:

Let me pass an UPDATE statement and observe how CDC records its changes in the audit tables as shown below.

--This script is compatible with SQL Server 2008 and above.
USE [AdventureWorks2012]
GO
--Update a record in [HumanResources].[Department]
USE [AdventureWorks2012]
GO
UPDATE [HumanResources].[Department]
SET [Name] = 'IT Support'
WHERE [DepartmentID]=17
GO

Once you UPDATE a record in the table ([HumanResources].[Department]), lets review the table ([HumanResources].[Department]) and its relevant audit table (cdc.HumanResources_Department_CT) respectively.

--This script is compatible with SQL Server 2008 and above.
USE AdventureWorks2012
GO
SELECT * FROM HumanResources.Department
GO
SELECT * FROM cdc.HumanResources_Department_CT
GO
--OUTPUT

Change data capture.2.2_part2

As you can observe from the above result set, it has one updated record in [HumanResources].[Department] as usual. In addition, two records have been inserted in the audit table (cdc.HumanResources_Department_CT) as well with some additional fields and ONE of the most important additional fields is _$operation that will explain you which operation inserted this record in the audit table. In the above result set say, _$operation has a value of 3 & 4 and it means that it has been inserted by UPDATE statement. But what do you mean by 3 & 4. In fact 3 means the data before the update statement and 4 means the data after the update statement.

  • Impact of DELETE STATEMENT in CDC:

Let me pass a DELETE statement and observe how CDC records its changes in the audit tables as shown below.

--This script is compatible with SQL Server 2008 and above.
USE [AdventureWorks2012]
GO
--Update a record in [HumanResources].[Department]
USE [AdventureWorks2012]
GO
DELETE from [HumanResources].[Department] WHERE [DepartmentID]=17
GO

Once you DELETE a record in the table ([HumanResources].[Department]), lets review the table ([HumanResources].[Department]) and its relevant audit table (cdc.HumanResources_Department_CT) respectively.

--This script is compatible with SQL Server 2008 and above.
USE AdventureWorks2012
GO
SELECT * FROM HumanResources.Department
GO
SELECT * FROM cdc.HumanResources_Department_CT
GO
--OUTPUT

Change data capture.2.3_part2

As you can observe from the above result set, it has DELETED one record in [HumanResources].[Department] as usual. In addition, ONE record has been inserted in the audit table (cdc.HumanResources_Department_CT) as well with some additional fields and ONE of the most important additional fields is _$operation that will explain you which operation inserted this record in the audit table. In the above result set say, _$operation has a value of 1 and it means that it has been inserted by DELETE statement.

In my upcoming article, I will write how to DISABLE the CDC feature.

An update of my blog is available at my twitter or you can like my Facebook page or subscribe via email by mentioning your email address in the ‘follow blog’ section.

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SQL SERVER – Working with Change Data Capture – Part 1

Posted in Audit, SQL SERVER, tagged , , , , , , , , on April 14, 2014| 3 Comments »

In general, if your application having an audit trial feature (to records any add, edit & delete activity performed by any end user in each table), it would be value addition to your application or it may be the best selling point of your application. However, when it comes to the development of this feature, it really become a nightmare. The reason for being problematic is that you need to integrate this feature everywhere in your application. In addition, you need to develop so many audit tables, stored procedures & triggers in order to achieve it. Sometimes the development and testing of this feature takes long time.
In SQL Server 2008, this problem has been solved by shipping a new feature namely Change data capture. It is one of the biggest and remarkable features in SQL Server 2008. In fact, it records and maintains all the changes in any table (if enabled) with very minimal amount of efforts and the good news is that the developers do not need to write even single a line of code to capture all these changes :).

In this article, I will demonstrate how to enable Change Data Capture (CDC) for any database and tables step by step.

Step 1 :
Before enabling CDC for any database, you must check whether it is already enabled or not. Given below is the script that shows all the databases along with its CDC enabled status.

--This script is compatible with SQL Server 2008 and above.
USE master
GO
SELECT
database_id,
name,
is_cdc_enabled
FROM sys.databases
GO
--OUTPUT

Change data capture.1.1_part1

Step 2 :
In step 1, as you observed that all the is_cdc_enabled columns of sys.database (system view) is 0. It means that none of the databases has been enabled for CDC.
Lets enable CDC for AdventureWorks2012 database in this step. Given below is the script.

--This script is compatible with SQL Server 2008 and above.
--DONOT forget to change the database name below.
USE AdventureWorks2012
GO
EXEC sys.sp_cdc_enable_db
GO

Step 3 :
Once you enabled the CDC, you need to repeat step 1, in order to check whether CDC has been enabled for AdventureWorks2012 database or NOT.
Given below is the same script but the output would be different.

--This script is compatible with SQL Server 2008 and above.
USE master
GO
SELECT
database_id,
name,
is_cdc_enabled
FROM sys.databases
GO
--OUTPUT

Change data capture.1.2_part1

As you can see that is_cdc_enabled column value is 1 for AdventureWorks2012 database and it is a confirmation that CDC is enabled for AdventureWorks2012 database.

Step 4 :
Once you enable the CDC in the database lets enable the CDC in a table in order to capture the changes in that particular table.
But hang on a minute, before activating this feature on any table, you must check whether it is already enabled for that particular table or not. Given below is the script that will list down all the tables available in that particular database along with the CDC status.

--This script is compatible with SQL Server 2008 and above.
USE AdventureWorks2012
GO
SELECT
object_id,
SCHEMA_NAME(Schema_id) As [Schema Name],
name As [Table Name],
is_tracked_by_cdc
FROM sys.tables
GO
--OUTPUT

Change data capture.1.4_part1

Step 5 :
In step 5, as you noticed that all the is_cdc_enabled columns of sys.database (system view) is 0. It means that none of the databases has been enabled for CDC.
Lets enable CDC for table namely HumanResources.Department in AdventureWorks2012 database in this step. Given below is the script.

--This script is compatible with SQL Server 2008 and above.
--DONOT forget to change the database name below.
USE AdventureWorks2012
GO
EXEC sys.sp_cdc_enable_table
@source_schema = N'HumanResources',
@source_name = N'Department',
@role_name = NULL
GO

As you can see above one of the parameters @role_name is NULL. I deliberately made it NULL, so all the users belonging to any role can view the changes in that particular table. However, you can pass any role to restrict the access from other users & roles accordingly.

Step 6 :
In this step, we need to check again if CDC has been enabled for that particular table or not. In order to do it, we need to repeat step 3 and this time the result set would be different. Given below is the same script as Step 4.

--This script is compatible with SQL Server 2008 and above.
USE AdventureWorks2012
GO
SELECT
object_id,
SCHEMA_NAME(Schema_id) As [Schema Name],
name As [Table Name],
is_tracked_by_cdc
FROM sys.tables
GO
--OUTPUT

Change data capture.1.5_part1

Step 7 :
Now, we assured that CDC has been enabled for that particular table, it means that CDC has created an audit table for that particular table (Same way we used to manually create in earlier version of SQL Server to record audit for any table). But where is that particular audit table ? You will find that particular table in CDC schema as shown below.

Change data capture.1.6_part1

In my upcoming article, I will write how to manipulate the CDC feature and how we can view those changes in order to really enjoy the audit trial feature with zero customization.

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