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 Some Sql Features
Trigger
Transaction
Batches
Stored Procedure

DML DDL
Trigger
What is Trigger?
A Trigger is a named database object which defines
some action that the database should take when
some databases related event occurs.
The trigger event can be any of the DML or DDL Statement:
INSERT
UPDATE
DELETE
CREATE TABLE
ALTER TABLE

The general syntax of CREATE TRIGGER is :
CREATE TRIGGER trigger_name trigger_time trigger_event
ON tbl_name FOR EACH ROW trigger_statement
[Trigger_statement have the statement that executes when the
trigger fires but if you want to execute multiple statement the you
have to use the BEGIN or END compound statement.]
Note:
The general syntax of DROP TRIGGER is :
DROP TRIGGER trigger_name

What is DML Trigger?
A DML Trigger is fired when data in the underlying table is
affected by DML statements, such as
INSERT,UPDATE,DELETE.
What is DDL Trigger?
A DDL trigger is fired to response to DDL statement,
such as CREATE TABLE or ALTER TABLE.
Depending on the way in which trigger are fired , they are
categorized as:
1. After Trigger 2. Nested Trigger
3. Instead of Trigger 4. Recursive Trigger

ALTER TRIGGGER trigger_name
{FOR|AFTER}{event_type[,...n] |
DDL_DATABASE_LEVEL_EVENTS}
{AS
{sql_statement[...n]}
}
Managing Triggers
 How can you manage triggers?
While managing triggers, you can perform the following
operations on a triggers:
1. Altering a trigger
2. Deleting a trigger
DROP TRIGGER trigger_name

Transactions
What is Transaction?
A transaction can be define as a sequence performed
together as a single logical unit of work.
A Single unit of work must process the four properties called
ACID.
Atomicity
Consistency
Isolation
Durability
A
C
I
D

The SQL Server allows implementing transactions in the following
two ways:
1. Autocommit Transaction
2. Explicit Transaction
Explicit transaction are specified by using two statement:
1. BEGIN TRANSACTION
2. COMMIT TRANSACTION
For example:-
BEGIN TRAN myTran
Select * From Humanresource.Department
COMMIT TRAN myTran

Reverting Transaction
At a time there is a possibility that due to a problem all the
statements of a transaction will not be successfully executed.
Client gets an
error with “Try
Again” msg
Client still
waiting
Transaction
timed out
For example:-
Client hit the
button to place
the orders
12:00 AM 12:02 AM 12:05 AM 12:08 AM 12:11 AM 12:14 AM
Then we use for resolving this problem:-
 ROLLBACK TRANSACTION:
ROLLBACK TRAN[SACTION] [transaction_name |
@tran_name_variable | savepoint_name |
@savepoint_variable]]

Transactional Integrity
To maintain the Security & Concurrency issues in giving Multi-user
Environment we use 'LOCKS'.
 Need For Locking:
In the absence of Locking, problems may occur if more then
one transaction use the same data from a database at the same
time.
These problem Include:-
1. Lost Updates
2. Uncommitted dependency(Dirty Read)
3. Inconsistent Analysis
4. Phantom Reads

 Controlling Locks
If you want to change the lock mode from a Normal shared lock to
an Exclusive lock you need use Isolation levels
Types of isolation levels are:
1. READ UNCOMMITED
2. READ COMMITED
3. REPEATABLE READ
4. SNAPSHOT
5. SERIALIZABLE
 Deadlocks Condition:
A Deadlock is a situation where two or more transaction have
locks on separate objects, and each transaction wait for a lock on
the other object to be released.

 Resolving Deadlocks:
To resolved the deadlock Situation we uses :-
1. Setting Deadlock Priority
SET DEADLOCK_PRIORITY{LOW|NORMAL|@deadlock_var}
2. Customizing Lock Timeout
SET LOCK_TIMEOUT [timeout_period]
3. Using sys.dm_exec_requests
SELECT * FROM sys.dm_exec_requests

Batches
What is Batches ?
A Batches is group of Sql statements submitted together to
the Sql Server for execution.
To create a batch, you can write multiple SQL statements
followed by the keyword GO at the end:-
<T-SQL Statement1>
<T-SQL Statement2>
<T-SQL Statement3>
......
GO
Note:- Go is the command that specifies the end of the batch
statement.

 Using Variables with Batches
While creating batches, you might need to save value
temporarily during the execution time then you define a variable
by DECLARE statement.
For example:-
DECLARE @variable_name data_type
 Guideline to Create Batches
You cannot combine statements, such as CREATE RULE,
CREATE TRIGGER etc, with other statements while
creating a batch.
You can use the EXECUTE statement in a batch when it is not
the 1st statement of the batch.

 Stored Procedures
A stored Procedure is a Pre-Compiled object stored in the
database.
The syntax of the create Procedure Statement is:-
CREATE PROCEDURE proc_name
AS
BEGIN
sql_statment1, sql_statement2
END
 Executing a Stored Procedure
A procedure can be executed by using the EXEC
PROCEDURE statement.
EXEC | EXECUTE PROCEDURE proc_name AS [{login|user} ='name']

 Altering a Stored Procedure
A Stored Procedure can be modified by using the ALTER
PROCEDURE statement.
Syntax:-
ALTER PROCEDURE proc_name
 Dropping a Stored Procedure
You can Drop the Stored Procedure from the Database by
using DROP PROCEDURE statement.
Syntax:-
DROP PROCEDURE proc_name

Creating Parameterized Stored procedures
When you need to Execute Procedure for different values of a
variable that provided at runtime. for this, you can create
parameterized store procedure.
Syntax:-
CREATE PROC prcListEmployee @title char(50)
AS
BEGIN
PRINT 'List of Employees'
SELECT EmployeeID, Login, Title from
HumanResource.Employee WHERE Title=@title
END
EXECUTE prcListEmployee @title=‘tool designer’

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ISAS On SQL Features like Trigger, Transaction,Batches, Stored Procedure

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ISAS On SQL Features like Trigger, Transaction,Batches, Stored Procedure