Covers Data Control Language Statements of SQL.

1. 7. DCL Statements of SQL
 Connection Management
 Transaction Management
 Access Control
 Session Management

2. DCL Statements of SQL
The DCL statements are used for the following purpose:
 Connection management
 Transaction management
 Access control
 Session management

3. DCL:
CONNECTION MANAGEMENT
Connection management statements are used to
start and stop connections to the RDBMS.

4. CONNECTION MANAGEMENT Statements
The connection management statements are:
 CONNECT statement
 SET CONNECTION statement
 DISCONNECT statement
Various RDBMSs either implement these statements in
their own way or do not implement these statements
but implement some other statements. Hence we do
not cover the SQL standard syntax here. Rather we
cover syntax used to connect to databases using
command line tools provided by MySQL.

5. Connection Management with MySQL
Connecting to MySQL Server
mysql is a command line tool to connect to MySQL server
and execute SQL statements.
Syntax: mysql [options] [db-name]
db-name: Name of a MySQL database
options: -? | -I | --help | -h host-name
| -u user-name
| -p | --password[=password-str]

6. Connection Management with MySQL
Examples
The right side screenshot
shows user “root” logged
into MySQL using command
line tool “mysql”, executed
a command USE to use
database “schdb” and
exited from the tool.
The second screenshot
shows that user “root”
specified database name
“schdb” on the command
line tool itself and hence
no need to execute USE
command explicitly to use
the database.

7. Connection Management with MySQL
Example with a new
User
The right side screenshot shows
super or root user “root” logged
into MySQL server without
specifying any database name,
created a user “suri” with
password “suri123”, gave SELECT
privilege on all tables of
database “schdb” and exited
from the command line tool.
The second screenshot shows
user “suri” logged into database
“schdb” by specifying password
on the command line of mysql
itself, accessed a table “dept”
and exited the tool.

8. Connection Management with MySQL
Connection Errors
The right side screenshot
shows that user can login
into MySQL server but can
not use a database if he
does not have privileges.

9. DCL:
TRANSACTION MANAGEMENT
 What is a Transaction?
 Transaction Statements
 Transaction Phenomena
 Isolation Level
 Transaction Characteristics
 Deferring Execution of Constraints

10. What is a Transaction ?
 An SQL Transaction is a logical unit of work
consisting of one or more SQL statements.
 Transactions are atomic.
 Transactions begin automatically by SELECT,
INSERT, UPDATE or DELETE statement or
explicitly by START TRANSACTION statement.
 Transactions are completed by either COMMIT
or ROLLBACK statement.

11. Transaction Examples
SELECT eno, ename, salary
FROM emp WHERE eno IN (555, 556);
UPDATE emp SET salary = 15000
WHERE eno IN (555, 556);
UPDATE emp SET salary = salary * 1.1
WHERE ename = ’Alishan’;
COMMIT;
SELECT eno, ename, salary
FROM emp WHERE eno IN (555, 556);

12. Transaction Management
Statements
Here are the transaction management statements:
START TRANSACTION
COMMIT
ROLLBACK
SET TRANSACTION
SET CONSTRAINTS

13. START TRANSACTION
The START TRANSACTION statement starts an SQL
transaction and sets its characteristics.
Syntax: START TRANSACTION
[ READ ONLY | READ WRITE ]
[ ISOLATION LEVEL { READ UNCOMMITTED } |
{ READ COMMITTED } | { REPEATABLE READ } |
{ SERIALIZABLE } ]
[ DIAGNOSTICS SIZE ncond ]

14. TRANSACTION ISOLATION LEVEL
Transaction Phenomena
To understand the isolation levels, we need to understand
the kind of phenomena that can occur while transactions are
executed concurrently:
Dirty read
Non-repeatable read
Phantom read

15. TRANSACTION ISOLATION LEVEL
Transaction Phenomena
Phenomena Description
Dirty Read Transaction T1 reads a row that has been changed by
another transaction T2 which has not yet committed. If T2
rolls back the transaction, T1 will have read the data that
never existed.
Non-repeatable
Read
Transaction T1 reads a row. Transaction T2 then modifies or
deletes that row and performs a COMMIT. If T1 then
attempts to reread the row, it may receive the modified
value or discover that the row has been deleted.
Phantom read Transaction T1 reads a set of rows N that satisfy some
search condition. Transaction T2 then executes SQL-
statements that generate one or more rows that satisfy the
search condition used by transaction T1. If transaction T1
then repeats the initial read with the same search
condition, it obtains a different collection of rows

16. TRANSACTION ISOLATION LEVEL
Vs TRANSACTION PHENOMENA
Isolation Level Dirty
Read
Non-repeatable
Read
Phantom
Read
READ UNCOMMITTED Y Y Y
READ COMMITTED N Y Y
REPEATABLE READ N N Y
SERIALIZABLE N N N
The following table shows the kind of phenomena that can
occur depending on the isolation level you set for
transactions using SET TRANSACTION ISOLATION LEVEL
statement.

17. COMMIT
The COMMIT statement ends a transaction successfully by
making database changes permanent.
Syntax: COMMIT [ WORK ]
The keyword WORK is optional.
Once the statement is executed by an RDBMS (server), all
database changes done by all other DDL or DML statements
executed before the COMMIT statement are made
permanent by the RDBMS.

18. ROLLBACK
The ROLLBACK statement aborts a transaction by backing
out all changes done in the transaction.
Syntax: ROLLBACK [ WORK ]
The keyword WORK is optional.
Once the statement is executed by an RDBMS (server), all
database changes done by all other DDL or DML statements
executed before the ROLLBACK statement are backed out or
undone by the RDBMS and the database is brought back to
the state it was before starting of the transaction.

19. SET TRANSACTION
The SET TRANSACTION statement sets properties or
characteristics of transactions.
Syntax: SET TRANSACTION [ READ ONLY | READ WRITE ]
[ ISOLATION LEVEL { READ UNCOMMITTED } |
{ READ COMMITTED } | { REPEATABLE READ } |
{ SERIALIZABLE } ]

20. SET CONSTRAINTS
The SET CONSTRAINTS statement sets constraint mode for
transactions.
You can use this statement to defer execution of any
constraints to the end of transaction.
Syntax: SET CONSTRAINTS { ALL | constraint-name-list }
{ DEFERRED | IMMEDIATE }
constraint-name-list:
constraint-name [, constraint-name]…
ALL : All constraints

21. SET CONSTRAINTS EXAMPLE
Schema

22. SET CONSTRAINTS EXAMPLE
INSERT Operation

23. Access Control
 Access Control Statements
 Authorization Identifier
 Privileges
 Granting and Revoking Privileges

24. ACCESS CONTROL
Statements
SQL supports discretionary data access control through
the following statements:
•GRANT
•REVOKE
GRANT: The statement is used to give privileges to other
users.
REVOKE: The statement is used to take away already
given privileges from other users.

25. ACCESS CONTROL
Authorization Identifiers
An authorization identifier is an SQL identifier used to
identify a database user.
Examples: john, praveen, akhilm and user1
• Each authorization identifier is usually associated
with a password.
• Every SQL statement executed by the RDBMS on
behalf of specific user.
• RDBMS uses authorization identifier to determine if
the user has access to a database object and if so
what kind access rights or privileges the user has.

26. ACCESS CONTROL
Privileges
The privileges are permissions that decide what action a
user can perform on a database table or view.
Here is the list of privileges defined in SQL standard:
Privilege Description
SELECT The privilege to retrieve data from a table.
INSERT The privilege to insert rows into a table.
UPDATE The privilege to update rows of a table.
DELETE The privilege delete rows from a table.
REFERENCES The privilege to reference columns of a table in integrity constraints.
USAGE The privilege to use domains. collations, character sets and translations.
EXECUTE The privilege to execute stored procedures or functions.

27. ACCESS CONTROL
GRANT Statement
The GRANT statement grants privileges on specified
database objects to specified users.
Syntax: GRANT {privilege_list | ALL PRIVILEGES}
ON object_name TO {auth_id_list | PUBLIC}
[WITH GRANT OPTION]
priv_list: SELECT [(col_name_list)] |
INSERT [(col_name_list)] | UPDATE [(col_name_list)] |
DELETE | REFERENCES [(col_name_list)] | USAGE |
TRIGGER | EXECUTE
object_name: Table, domain , etc. (depends on privilege)
auth_id_list: List of user authorization identifiers
col_name_list: Comma separated column names

28. GRANT Statement
Example - Users
(1) Users: User Name Password
system system123
akhil akhil123
john john123
(2) The following screen shot shows
creating the users using SqlPlus of
Oracle:
(3) The following screen shot
shows akhil does not have
privileges to use two tables:

29. GRANT Statement
Examples - Privileges
(1) Granting privileges to akhil
and public:
(2) Testing
privileges
of john.
(3) Testing privileges of akhil:

30. ACCESS CONTROL
REVOKE Statement
The REVOKE statement revokes privileges on specified
database objects from specified users.
Syntax: REVOKE [GRANT OPTION FOR]
{privilege_list | ALL PRIVILEGES}
ON object_name
FROM {auth_id_list | PUBLIC} [RESTRICT | CASCADE]
priv_list: SELECT [(col_name_list)] | INSERT [(col_name_list)] |
UPDATE [(col_name_list)] | DELETE |
REFERENCES [(col_name_list)] | USAGE | TRIGGER | EXECUTE
object_name: Table, domain , etc. (depends on privilege)
auth_id_list: List of user authorization identifiers
col_name_list: Comma separated column names

31. REVOKE Statement
Examples - Privileges
(1) Revoke SELECT
privilege from akhil: (2) Revoke UPDATE privileges
from PUBLIC on table depttbl:

32. What Have You Learnt!
• Connecting to Databases.
• How to connect to MySQL Databases.
• What is a Transaction?
• When Transactions begin ?
• Transaction Statements START TRANSACTION, COMMIT and ROLLBACK.
• SET TRANSACTION and SET CONSTRAINTS statements.
• Transaction Isolation Levels
• Transaction Phenomena – Dirty Read, Non-repeatable Read and Phantom
Read
• Access Control, Authorization ID
• Privileges SELECT, INSERT, UPDATE, DELETE, REFERENCES, USAGE and
EXECUTE.
• Granting and revoking privileges using GRANT and REVOKE statements.