TCL &DCL

Transaction Control Language:-

1. Transaction is a logic unit of work
2. Whatever the changes we made to the DataBase can be referred as a Transaction.
3. Whenever we perform a DML operation like select,update,insert ,delete the results will be stored in Buffer .But not in Permanent Database .
4. The user Can control the transaction changes with the use of  TCL Commands

1}Commit

2}RollBacka

3}Save Transaction

In general these commands are used for managing the changes affecting the data.

1)Commit:-

It is used to save the work Done /Used to Make changes permanently SY:-Begin Transaction Transaction Name

2)Rollback:-

    This Command is used to restore the database to original since the last Commit.

     Rollback command can only be used to Undo transactions since last                .........commit/Rollback Command was used.

      SY:-Rollback Transaction Transaction Name

3)SavePoint:-

    It is a mechanism to rollback portion of transactions

    In general Savepoint is used to create points within group of transactions which to ......Rollback.

1.Ex

          begin transaction sampath—creating a transaction

          after creating the transaction iam deleting the records like

          delete from employee where empid=1

          delete from employee where empid=3

          rollback transaction sampath

2.Ex

          begin transaction krishna

          insert into employee values(3,'parveen',90000)

          insert into employee values(3,'krishna',22000)

          commit transaction krishna

          select *  from employee

          rollback transaction krishna

Data Control Language:-

These Sql Commands are used for providing the security to database objects.

1)Grant

2)Revoke

(1)Grant:- 
This command is used for give access privileges to users for database

Previleges are:-Select ,Insert,Update,Delete.

Syntax:-Grant <Previleges>  on <Table Name > to <Users> [with Grant Option]

Ex:-Grant select,insert on Employee to Krishnaveni

(2)Revoke:-

These commands are Used for Withdraw access privileges to users for database.

Sy:-Revoke <Privileges > on Table Name from <users>

Ex:-revoke select,insert on Employee from Krishnaveni Cascade