Triggers in SQL Server

Triggers

Creates a DML, DDL, or logon trigger. A trigger is a special kind of stored procedure that automatically executes when an event occurs in the database server. DML triggers execute when a user tries to modify data through a data manipulation language (DML) event. DML events are INSERT, UPDATE, or DELETE statements on a table or view.

DML Triggers

DML triggers are frequently used for enforcing business rules and data integrity. SQL Server provides declarative referential integrity (DRI) through the ALTER TABLE and CREATE TABLE statements. However, DRI does not provide cross-database referential integrity. Referential integrity refers to the rules about the relationships between the primary and foreign keys of tables. To enforce referential integrity, use the PRIMARY KEY and FOREIGN KEY constraints in ALTER TABLE and CREATE TABLE. If constraints exist on the trigger table, they are checked after the INSTEAD OF trigger execution and before the AFTER trigger execution. If the constraints are violated, the INSTEAD OF trigger actions are rolled back and the AFTER trigger is not fired.

DDL Triggers

In your workplace does more than one person has access to databases that are vital to the smooth operation of your organisation? Do these users have rights to alter the database structure by using Data Definition Language (DDL) statements such as CREATE TABLE..., DROP TABLE etc?

If the answer to the above questions are yes then are mechanisms in place to help monitor/audit who is making what changes to the database? Who deleted that table? Who changed that columns data type? What code was in the previous version of that procedure that now isn't working? This type of auditing is being asked for more and more as organisations become more and more dependent on their databases for helping in all aspects of day to day work.

DDL Triggers (introduced in SQL Server 2005) provide you with the capability of auditing the creation, deletion and modification of database objects as well as other capabilities such as checking that DDL code conforms to your business rules before executing it.

How Triggers work

A Trigger is a block of T-SQL code that is executed or 'triggered' as a result of another statement that is sent to the database. Before SQL Server 2005 a trigger could be 'triggered' by either INSERT, UPDATE or DELETE (Data Manipulation Language - DML) statements. SQL Server 2005 introduced DML Triggers that can be set to fire on your chosen DDL events such as CREATE_TABLE, ALTER_TABLE, DROP_TABLE, ALTER_DATABASE, CREATE_LOGIN etc.

DDL Triggers can be set with either a Server scope or database scope. Triggers created with Server scope must target server DDL events such as CREATE_DATABASE or CREATE_LOGIN whilst triggers created with database scope must target database level events such as CREATE_TABLE or ALTER_PROC. See the full list of SQL Server DDL Trigger Events (including their scope).

DDL triggers can only fire after the DDL statement has occurred. This is different from DML triggers which can fire before the triggering statement.

Syntax of a DDL trigger

CREATE TRIGGER [TriggerName]
ON [Scope (Server|Database)]
FOR [EventName...],
AS
-- code for your trigger response here

The EventData function

If you want to audit changes to your database schemas you need to be able to access the triggering events in your DDL trigger so that you can record what changes are being made. To access the triggering event we can use the EventData function in our DDL trigger. The EventData function returns an xml value.

The EventData xml value includes the triggering SQL statement, the event time, the type of event and depending on what type of event was called, extra information such as the database name. The following example shows how EventData can be used to record all statements that changed the table or stored proc schemas into a table called DDLAudit.

CREATE TRIGGER AuditProcChanges
ON DATABASE
FOR CREATE_PROC, ALTER_PROC, DROP_PROC, CREATE_TABLE, ALTER_TABLE, DROP_TABLE
AS

DECLARE @ed XML
SET @ed = EVENTDATA()

INSERT INTO DDLAudit (PostTime, DatabaseName, Event, ObjectName, TSQL, Login)
VALUES
(
GetDate(),
@ed.value('(/EVENT_INSTANCE/DatabaseName)[1]', 'varchar(256)'),
@ed.value('(/EVENT_INSTANCE/EventType)[1]', nvarchar(100)'),
@ed.value('(/EVENT_INSTANCE/ObjectName)[1]', 'varchar(256)'),
@ed.value('(/EVENT_INSTANCE/TSQLCommand)[1]', 'nvarchar(2000)'),
@ed.value('(/EVENT_INSTANCE/LoginName)[1]', 'varchar(256)')
)

The EventData function returns an xml value and is assigned to a variable called @ed which is of an xml data type. The xquery function value(Xquery, sqltype) returns the specified values from the xml variable. For more information on EventData see MSDN.

This DDLAudit table could reside in the individual database or you could create a seperate ApplicationAudit database and use a 3 part name to record the audit in this ApplicationAudit database, i.e. INSERT INTO ApplicationAudit.dbo.DDLAudit ....

Covering all databases and events

If you wanted to audit the DDL events for all your databases you would need to create this trigger in each database. The above trigger only monitors DDL events that affect Tables and Stored Procedures. You can use the handy event name of DDL_DATABASE_LEVEL_EVENTS to make sure your trigger covers all DDL events that have database scope as follows:

CREATE TRIGGER AuditDBScopeDDLChanges
ON DATABASE
FOR DDL_DATABASE_LEVEL_EVENTS
AS
-- trigger code here...

Preventing DDL actions using triggers

Sometimes you may want to prevent the alteration of a schema, because the triggering statement and trigger are joined in one transaction we can call ROLLBACK in our trigger to rollback the DDL statement that caused the trigger to fire:

CREATE TRIGGER PreventDropTable
ON DATABASE
FOR DROP_TABLE
AS
PRINT 'Tables cannot be dropped'
ROLLBACK

What happens if you then want to drop a table in the database with the above trigger? You can disable the trigger, drop the table and then re-enable the trigger:

DISABLE TRIGGER PreventDropTable
ON DATABASE
GO
DROP TABLE MyTable
GO
ENABLE TRIGGER PreventDropTable
ON DATABASE
GO

You could also if you wished extend use this method of schema change prevention for server scope events to prevent the dropping of databases:

CREATE TRIGGER PreventDropDatabaseServerWide
ON ALL SERVER
FOR DROP_DATABASE
AS
PRINT 'Cannot drop tables, DDL Trigger will rollback'
ROLLBACK

Finding DDL triggers using system tables

To view the DDL triggers in your databases of database scope you can query the sys.triggers table. To view the DDL triggers with server scope you need to query the sys.server_triggers table in the master database.

Conclusion

When designing your DDL trigger you will probably be performing one of more of the following actions:

• Recording changes made to the database schema
• Stopping certain types of changes being made to the database schema
• Fire another action in the database in response to the schema change

We have seen how DDL triggers can be used to a) audit and b) control schema changes using the EventData function and the ROLLBACK command respectively.

Logon Triggers

Logon triggers fire in response to the LOGON event. This event is raised when a user sessions is being established. For more information.

Multiple Triggers

SQL Server allows for multiple triggers to be created for each DML, DDL, or LOGON event. For example, if CREATE TRIGGER FOR UPDATE is executed for a table that already has an UPDATE trigger, an additional update trigger is created. In earlier versions of SQL Server, only one trigger for each INSERT, UPDATE, or DELETE data modification event is allowed for each table.

Recursive Triggers

SQL Server also allows for recursive invocation of triggers when the RECURSIVE_TRIGGERS setting is enabled using ALTER DATABASE.

Nested Triggers

Triggers can be nested to a maximum of 32 levels. If a trigger changes a table on which there is another trigger, the second trigger is activated and can then call a third trigger, and so on. If any trigger in the chain sets off an infinite loop, the nesting level is exceeded and the trigger is canceled. To disable nested triggers, set the nested triggers option of sp_configure to 0 (off). The default configuration allows for nested triggers. If nested triggers is off, recursive triggers is also disabled, regardless of the RECURSIVE_TRIGGERS setting set by using ALTER DATABASE.

Drop all objects in a database on SQL Server

Solution for Drop all objects from database at once!

Following procedure run on any database (SQL Server)

\***********************************************/


CREATE PROCEDURE dbo.DropAllDBObjects
@Action VARCHAR(20)=NULL
As
BEGIN

DECLARE @Name VARCHAR(500)

IF @Action='Table'
BEGIN
DECLARE DROPALL CURSOR
FOR SELECT [NAME] FROM sys.TABLES

OPEN DROPALL
FETCH NEXT FROM DROPALL INTO @Name
WHILE @@FETCH_STATUS=0
BEGIN
EXEC('DROP TABLE ' + @Name)
FETCH NEXT FROM DROPALL INTO @Name
END
CLOSE DROPALL
DEALLOCATE DROPALL

END

ELSE IF @Action='PROCEDURE'
BEGIN
DECLARE DROPALL CURSOR
FOR SELECT [NAME] FROM sys.objects WHERE TYPE='P'

OPEN DROPALL
FETCH NEXT FROM DROPALL INTO @Name
WHILE @@FETCH_STATUS=0
BEGIN
IF @Name <> 'DropAllDBObjects'
EXEC('DROP PROCEDURE ' + @Name)
FETCH NEXT FROM DROPALL INTO @Name
END
CLOSE DROPALL
DEALLOCATE DROPALL

END
ELSE IF @Action='Function'
BEGIN
DECLARE DROPALL CURSOR
FOR SELECT SPECIFIC_NAME FROM INFORMATION_SCHEMA.ROUTINES WHERE ROUTINE_TYPE='FUNCTION'

OPEN DROPALL
FETCH NEXT FROM DROPALL INTO @Name
WHILE @@FETCH_STATUS=0
BEGIN
EXEC('DROP FUNCTION ' + @Name)
FETCH NEXT FROM DROPALL INTO @Name
END
CLOSE DROPALL
DEALLOCATE DROPALL

END
ELSE IF @Action='View'
BEGIN
DECLARE DROPALL CURSOR
FOR SELECT TABLE_NAME FROM INFORMATION_SCHEMA.VIEWS

OPEN DROPALL
FETCH NEXT FROM DROPALL INTO @Name
WHILE @@FETCH_STATUS=0
BEGIN
EXEC('DROP VIEW ' + @Name)
FETCH NEXT FROM DROPALL INTO @Name
END
CLOSE DROPALL
DEALLOCATE DROPALL

END
IF @Action is null
BEGIN
--Table
DECLARE DROPALL CURSOR
FOR SELECT [NAME] FROM sys.TABLES

OPEN DROPALL
FETCH NEXT FROM DROPALL INTO @Name
WHILE @@FETCH_STATUS=0
BEGIN
EXEC('DROP TABLE ' + @Name)
FETCH NEXT FROM DROPALL INTO @Name
END
CLOSE DROPALL
DEALLOCATE DROPALL

--Views
DECLARE DROPALL CURSOR
FOR SELECT TABLE_NAME FROM INFORMATION_SCHEMA.VIEWS

OPEN DROPALL
FETCH NEXT FROM DROPALL INTO @Name
WHILE @@FETCH_STATUS=0
BEGIN
EXEC('DROP VIEW ' + @Name)
FETCH NEXT FROM DROPALL INTO @Name
END
CLOSE DROPALL
DEALLOCATE DROPALL

--Functions
DECLARE DROPALL CURSOR
FOR SELECT SPECIFIC_NAME FROM INFORMATION_SCHEMA.ROUTINES WHERE ROUTINE_TYPE='FUNCTION'

OPEN DROPALL
FETCH NEXT FROM DROPALL INTO @Name
WHILE @@FETCH_STATUS=0
BEGIN
EXEC('DROP FUNCTION ' + @Name)
FETCH NEXT FROM DROPALL INTO @Name
END
CLOSE DROPALL
DEALLOCATE DROPALL

--Procedure
DECLARE DROPALL CURSOR
FOR SELECT [NAME] FROM sys.objects WHERE TYPE='P'

OPEN DROPALL
FETCH NEXT FROM DROPALL INTO @Name
WHILE @@FETCH_STATUS=0
BEGIN
IF @Name <> 'DropAllDBObjects'
EXEC('DROP PROCEDURE ' + @Name)
FETCH NEXT FROM DROPALL INTO @Name
END
CLOSE DROPALL
DEALLOCATE DROPALL
END
END
GO

\***********************************************/

To execute Procedure:

a)To Drop all objects from Database,execute following

EXEC DropAllDBObjects

b)To Drop all objects from Database,based on different object at time.

EXEC DropAllDBObjects 'table'

or

EXEC DropAllDBObjects 'View'

or

EXEC DropAllDBObjects 'Function'

or

EXEC DropAllDBObjects 'Procedure'


To View all objects,use following

SELECT [NAME] FROM sys.TABLES
SELECT [NAME] FROM sys.objects WHERE TYPE='P'
SELECT SPECIFIC_NAME FROM INFORMATION_SCHEMA.ROUTINES WHERE ROUTINE_TYPE='FUNCTION'
SELECT TABLE_NAME FROM INFORMATION_SCHEMA.VIEWS

After All work done,you can drop following procedure

DROP PROC DropAllDBObjects

Differences between varchar and nvarchar in SQL Server

The broad range of data types in SQL Server can sometimes throw people through a loop, especially when the data types seem to be highly interchangeable. Two in particular that constantly spark questions are VARCHAR and NVARCHAR: what's the difference between the two, and how important is the difference?

VARCHAR is an abbreviation for variable-length character string. It's a string of text characters that can be as large as the page size for the database table holding the column in question. The size for a table page is 8,196 bytes, and no one row in a table can be more than 8,060 characters. This in turn limits the maximum size of a VARCHAR to 8,000 bytes.

The "N" in NVARCHAR means uNicode. Essentially, NVARCHAR is nothing more than a VARCHAR that supports two-byte characters. The most common use for this sort of thing is to store character data that is a mixture of English and non-English symbols — in my case, English and Japanese.

The key difference between the two data types is how they're stored. VARCHAR is stored as regular 8-bit data. But NVARCHAR strings are stored in the database as UTF-16 — 16 bits or two bytes per character, all the time — and converted to whatever codepage is being used by the database connection on output (typically UTF-8). That said, NVARCHAR strings have the same length restrictions as their VARCHAR cousins — 8,000 bytes. However, since NVARCHARs use two bytes for each character, that means a given NVARCHAR can only hold 4,000 characters (not bytes) maximum. So, the amount of storage needed for NVARCHAR entities is going to be twice whatever you'd allocate for a plain old VARCHAR.

Because of this, some people may not want to use NVARCHAR universally, and may want to fall back on VARCHAR — which takes up less space per row — whenever possible.

Windows Vista Error Fix Desktop Icons And Taskbar Fails To Load At Startup

There are really a lot of reasons why all of your icons and your Windows Vista desktop fails, all of a sudden, to load at startup. Some times the taskbar also refuses to load at Windows Vista startup.Anyway, most of the times this issue is due to a little key in the registry called explorer.exe which refuses to load or it is just missing or it doesn’t exist at all.This Issue in Windows Vista is easily fixed by using one of these 4 fixes:

The following method i have checked out and its worked for my laptop inspiron 1545 windows vista home edition.

Method1:

Copy and paste the following piece of code in your notepad:

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon]
“Userinit”=”C:\\WINDOWS\\SYSTEM32\\userinit.exe,”

Now save the file as Userinit.reg. Double-click on it to merge it in the Windows Vista registry. or Change registry key value and close registry editor and restart.

Method 2:

The key Explorer.exe in your registry is not correct.To fix this:

• Click on Windows Vista Start.
• In the start menu Search Box type “regedit” and hit Enter.
• In Windows registry, locate the following key: [HKEY_LOCAL_MACHINE\ SOFTWARE\Microsoft\Windows NT\CurrentVersion\ Image File Execution Options]
• Look for Explorer.exe.
• Delete it.
• or Change registry key value to Explorer.exe to the above location and close registry editor then restart.

Method 3:

Restore Explorer.exe which is missing in your Windows Vista registry.To do this:

• Copy this piece of code in your notepad editor.

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon]
“Shell”=”explorer.exe”

• Save the file as Logon.reg.
• Double-click on it to merge it in the Windows Vista registry(Sometimes UAC prompt appears and click “Continue”).
• or Change registry key value to Explorer.exe to the above location and close registry editor then restart.

Method 4:

If explorer.exe is not in C:\WINDOWS\ then insert your Windows CD and, using the ‘Task Manager’ (File -> New Task), run the ‘System File Checker’ utility with this command:

sfc /scannow

If the ‘System File Checker’ didn’t replace it, boot to the Recovery Console with the Windows CD and copy explorer.exe manuallyFor this:

• Insert your Windows Vista DVD.
• When the setup screen window appears, choose the Repair or Recover option by pressing “R”.
• In the Command Prompt, type the following command: expand G:\i386 /F:EXPLORER.EX_ C: \WINDOWS\explorer.exe /y (don’t forget that G: is the letter of your DVD drive, while C: is the partition where Windows Vista is installed, change them if they are different in your PC)

original link from:

http://www.tomstricks.com/windows-vista-error-fixdesktop-icons-and-taskbar-fails-to-load-at-startup/

Identify last statement run for a specific SQL Server session

SELECT DEST.TEXT
FROM sys.[dm_exec_connections] SDEC
CROSS APPLY sys.[dm_exec_sql_text](SDEC.[most_recent_sql_handle]) AS DEST
WHERE SDEC.[most_recent_session_id] = (SELECT @@SPID)

RESEED All Identity Column in all tables of a Database

IF EXISTS(SELECT *FROM SYS.PROCEDURES WHERE NAME='SP_RESEEDIdentityColumn')
BEGIN
DROP PROC SP_RESEEDIdentityColumn
END
GO
CREATE PROC SP_RESEEDIdentityColumn
@RESEEDVALUE INT=0
AS
BEGIN
DECLARE CURRESEED CURSOR
FOR
SELECT NAME FROM SYS.TABLES

DECLARE @TABNAME VARCHAR(225),@SQL NVARCHAR(225)

OPEN CURRESEED
FETCH NEXT FROM CURRESEED INTO @TABNAME
WHILE @@FETCH_STATUS=0
BEGIN
SET @SQL ='DBCC CHECKIDENT('+@TABNAME+',RESEED,'+@RESEEDVALUE+')'
EXEC(@SQL)
FETCH NEXT FROM CURRESEED INTO @TABNAME
END
END

CLOSE CURRESEED
DEALLOCATE CURRESEED
GO


--Here if you are not specified param value it reseed from 0
EXECUTE SP_RESEEDIdentityColumn

--Here if you are not specified param value it reseed from 1
EXECUTE SP_RESEEDIdentityColumn 1

Delete the data from all tables In Database-Simple Sql Server Query!

USE TEST
EXEC sp_MSForEachTable 'ALTER TABLE ? NOCHECK CONSTRAINT ALL'
GO
EXEC sp_MSForEachTable '
IF OBJECTPROPERTY(object_id(''?''), ''TableHasForeignRef'') = 1
DELETE FROM ?
else
TRUNCATE TABLE ?
'
GO
EXEC sp_MSForEachTable 'ALTER TABLE ? CHECK CONSTRAINT ALL'
GO

Different String Function in SQL Server 2005

ASCII function in SQLServer

Returns the ASCII code value of Leftmost charector in a string
Syntax : ASCII ('char Expression')

NCHAR function in SQLServer
Returns the Unicode Charector with specified Integer code, as defined be Unicode standard
Syntax :NCHAR(Integer Expression)

SOUNDEX function in SQLServer
Returns a four-charector code to evalute the similarity of two strings
Syntax : SOUNDEX('char Expression')
Ex:
Select SOUNDEX('smith'),SOUNDEX('smythe')
Result:
S530 S530

CHAR function in SQLServer
Convert an Int ASCII code to a Charector
Syntax : CHAR( Integer Expression )
Note : Is an integer from 0 through 255, NULL is return if the integer expression not in the Range

PATINDEX function in SQLServer
Returns the starting position of the first occurance of a pattren in the specied expression, or Zero if the pattren is nor found the specified expression, on all valid text and charector data types.
Syntax : PATINDEX('%pattren%',expression)

SPACE function in SQLServer
Returns a string of Repeated Spaces
Syntax : SPACE (Integer Expression)
Ex:
Select 'Myname' + Space(2) + 'Lastname'
Result:
Myname Lastname

QUOTENAME function in SQLServer
Returns a Unicode string with the delimiters added to make the input string a valid Microsoft SQL Server delimited identifier
Syntax: QUOTENAME ( 'character_string' [ , 'quote_character' ] )

' character_string '

Is a string of Unicode character data. character_string is sysname and is limited to 128 characters. Inputs greater than 128 characters return NULL.

' quote_character '

Is a one-character string to use as the delimiter. Can be a single quotation mark ( ' ), a left or right bracket ( [] ), or a double quotation mark ( " ). If quote_character is not specified, brackets are used.

Ex:
Select QUOTENAME('abc[]def')
Result :
[abc[]]def

STR function in SQLServer
Returns characters data converted from numaric data
Syntax : STR (float Expression [,length,[[decima]])
Ex;
Select STR(123.45,6,1)
Result
123.4

DIFFERENCE function in SQLServer
Retruns interger value that indicates the difference between SOUNDEX value of two character expressions
Syntax : DIFFERENCE (firat expression, second Expression)

REPLACE function in SQLServer
Replaces all occurences of Specified string value with another string value
Syntax : Replace (car expression,old string,new string)
EX:
Print REPLACE('abcdefghcd','c','x')
Result:
abxdefghxd

STUFF function in SQLServer
Deletes a specied length of characters and insert another set of characters at specified starting point
Syntax : STUFF(char expression,start,length,char expression)
Ex :
select STUFF('abcdef',2,3,'ijklmn')
Result:
aijklmnef


LEFT function in sqlserver
Return the left part of the char expression with specied number of characters
Syntax : LEFT(char expression,length)
Ex:
print LEFT('abcdef',2)
Result:
ab

REPLICATE function in SQLServer
Replicate a string value in specified numver of times
Syntax : REPLICATE(char expression, interger expression)
Ex:
Print REPLICATE('0',4) + 'S'
Result:
0000S

SUBSTRING function in SQL Server
Returns a part of charecter, byte, text or Image expression
Syntax : SUBSTRING(char expression,start,length)
Ex:
select SUBSTRING('myname',1,2)
Result:
my

LEN function in SQL Server
Returns length of specified char expression, excluding trailing blank spaces
Syntax : LEN(char expression)
Ex :
print LEN(' my Name')
Result :
7


REVERSE function in SQL Server
Returns reverse of char expression
Syntax : REVERSE(char expression)

Create your own key in Registry using Microsoft.Win32.RegistryKey in c#.Net

//Check for key exists in Registry before creating New key and if not exists then create new key

if (((Microsoft.Win32.RegistryKey)(Microsoft.Win32.Registry.CurrentUser.OpenSubKey("MyChandruKey123"))) == null)

{

Microsoft.Win32.RegistryKey key = Microsoft.Win32.Registry.CurrentUser.CreateSubKey("MyChandruKey123");

key.SetValue("MyConnStrChandru123","");

}

//Get the Key value based on key name

string conns = ((Microsoft.Win32.RegistryKey)(Microsoft.Win32.Registry.CurrentUser.OpenSubKey("MyChandruKey123"))).GetValue("MyConnStrChandru123").ToString();

Encrypt and Decrypt the string using RSACryptoServiceProvider in c#.Net within Single Line of Code

//Call the functions

string EncryptedString= GetEncryptedText("Chandru");

string DecryptedString = GetDecryptedText(EncryptedString);

//Create an object for RSACryptoServiceProvider

RSACryptoServiceProvider RSAEncrypt = new RSACryptoServiceProvider();

//Encrypt the String Provided

public string GetEncryptedText(string PlainStringToEncrypt)

{

return Encoding.Default.GetString(RSAEncrypt.Encrypt(Encoding.Default.GetBytes(PlainStringToEncrypt), false));

}

//Decrypt The String Provided

public string GetDecryptedText(string EncryptedStringToDecrypt)

{

return Encoding.Default.GetString(RSAEncrypt.Decrypt(Encoding.Default.GetBytes(EncryptedStringToDecrypt), false));

}