Introduction to SQL Server

Transactions and DCL statements

Transactions

Relevance of Transactiontbl_login

pk_user_id username password1 John Admin123

2 alex Alex123

tbl_userpk_user_id fk_user_id user_name user_dob

1 2 Alex 1995-12-122 1 John 1995-09-21

• In the above tables, Whenever a user register, entry must go into both tbl_user and tbl_login.

• There should not be a situation with entry in only one table . ie user without login details or login details without any user information

• This means whenever we enter data into these tables, we should make sure entry is done for both table or to neither tables

Transactions

• A transaction is a sequential group of database manipulation operations, which is performed as if it were one single work unit.

• In other words, a transaction will never be complete unless each individual operation within the group is successful. If any operation within the transaction fails, the entire transaction will fail.

Create procedure sample()

Begin

declare @a int;

declare @b int;

START TRANSACTION

Insert into tbl_login values(‘john’,’john123’);

Set @a = scope_identity();

Insert into tbl_user values(a,’john mathew’,1980-12-13);

Set @b = scope_identity();

if(@a>0&&@b>0)

begin

COMMIT TRANSACTION end

ELSE begin

ROLLBACK TRANSACTION end

Will start a new transaction. So any sql operations will get effected until we give commit or rollback

Create procedure sample()

Begin

Declare @a int;Declare @b int

START TRANSACTION

Insert into tbl_login values(‘john’,’john123’);

Set @a = scope_identity();

Insert into tbl_user values(a,’john mathew’,1980-12-13);

Set @b = scope_identity();

If @a>0 && @b>0 THEN

COMMIT TRANSACTION

ELSE begin

ROLLBACK end

End

Will make the changes permanently

Create procedure sample()Begin

begin try

BEGIN TRANSACTIONInsert into tbl_login values(‘john’,’john123’);Insert into tbl_user values(’john mathew’,1980-12-13);

COMMIT TRANSACTIONend try

begin catch

ROLLBACK TRANSACTIONend catch

End

Transactions with declare handler

Questions?“A good question deserve a good

grade…”

Self Check !!

• Why should someone use Transaction?

– To ensure data redundancy– To reduce network traffic between application

server and database server– To ensure data integrity

Self Check !!

• Why should someone use Transaction?

– To ensure data redundancy– To reduce network traffic between application

server and database server– To ensure data integrity

Self Check !!

• Why should someone use Transaction?

– To ensure data redundancy– To reduce network traffic between application

server and database server– To ensure data integrity

Self Check !!

Create Procedure insertData()Begin

DECLARE done default 0;BEGIN TRYBEGIN TRANSACTION

Insert into tbl_login(pk_int_id,vchr_uname,vchr_pword) values(1,’john123’,’321’);Insert into tbl_user (vchr_name,dat_dob) values(’john mathew’,’1980-12-13’);

COMMIT TRANSACTIONEND TRYBEGIN catchROLLBACK END catchEnd

Will it be committed or rolled back? And reason? when it will be happened

Create Procedure insertData()Begin

begin tryBEGIN TRANSACTION;Insert into tbl_login(pk_int_id,vchr_uname,vchr_pword) values(1,’john123’,’321’);Insert into tbl_user (vchr_name,dat_dob) values(’john mathew’,’1980-12-13’);

COMMITEND TRANSACTIONend tryBEGIN CATCHROLLBACK END catch

EndIFEnd

Will it be committed or rolled back? And reason? when it will be happened

Things will work fine (commited)when you call the SP for the first time. But for the second time onwards it will

keep roll back as the table already has the same primary key and hence SQLWARNING will be triggered

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