PLSQL- Assertion , Roles & Privileges,

Embedded & Dynamic SQL

Assertion

• Assertions - An assertion is a piece of SQL which makes sure a condition is satisfied or it stops action being taken on a database object. It could mean locking out the whole table or even the whole database.

• Assertions - Assertions do not modify the data, they only check certain conditions.

Assertion

Syntax:

CREATE ASSERTION <name>

CHECK ( <condition> );

Example: Assertion

There should not any customer in bank having balance less than 1000. Create Assertion c1 Check

( NOT EXISTS (

Select *

From customer

Where balance<1000));

Roles & Privileges

Controlling User Access

Database

administrator

Users

Username and password

Privileges

Privileges

• Database security:

• System security

• Data security

• System privileges: Gaining access to the database

• Object privileges: Manipulating the content of the database objects

• Schemas: Collection of objects such as tables, views, and sequences

System Privileges

• More than 100 privileges are available.

• The database administrator has high-level system privileges for tasks such as:

• Creating new users

• Removing users

• Removing tables

• Backing up tables

Creating Users

The DBA creates users with the CREATE USER statement.

CREATE USER HR

IDENTIFIED BY HR;

User created.

CREATE USER user

IDENTIFIED BY password;

User System Privileges

After a user is created, the DBA can grant specific system privileges to that user.

An application developer, for example, may have the following system privileges:

CREATE SESSION

CREATE TABLE

CREATE SEQUENCE

CREATE VIEW

CREATE PROCEDURE

GRANT privilege [, privilege...]

TO user [, user| role, PUBLIC...];

Granting System Privileges

The DBA can grant specific system privileges to a user.

GRANT create session, create table,

create sequence, create view

TO scott;

Grant succeeded.

Creating and Granting Privileges to a Role

• Create a role

• Grant privileges to a role

• Grant a role to users

CREATE ROLE manager;

Role created.

GRANT create table, create view

TO manager;

Grant succeeded.

GRANT manager TO DE HAAN, KOCHHAR;

Grant succeeded.

Object Privileges

• Object privileges vary from object to object.

• An owner has all the privileges on the object.

• An owner can give specific privileges on that owner’s object.

GRANT object_priv [(columns)]

ON object

TO {user|role|PUBLIC}

[WITH GRANT OPTION];

Granting Object Privileges

Grant query privileges on the EMPLOYEES table.

Grant privileges to update specific columns to users and roles.

GRANT select

ON employees

TO sue, rich;

Grant succeeded.

GRANT update (department_name, location_id)

ON departments

TO scott, manager;

Grant succeeded.

Passing On Your Privileges

• Give a user authority to pass along privileges.

• Allow all users on the system to query data from Alice’s DEPARTMENTS table.

GRANT select, insert

ON departments

TO scott

WITH GRANT OPTION;

Grant succeeded.

GRANT select

ON alice.departments

TO PUBLIC;

Grant succeeded.

Revoking Object Privileges

• You use the REVOKE statement to revoke privileges granted to other users.

• Privileges granted to others through the WITH GRANT OPTION clause are also revoked.

REVOKE {privilege [, privilege...]|ALL}

ON object

FROM {user[, user...]|role|PUBLIC}

[CASCADE CONSTRAINTS];

Revoking Object Privileges

• As user Alice, revoke the SELECT and INSERT privileges given to user Scott on the DEPARTMENTS table.

REVOKE select, insert

ON departments

FROM scott;

Revoke succeeded.

Summary

In this lesson, you should have learned about statements that control access to the database and database objects.

Statement Action

CREATE USER Creates a user (usually performed by a DBA)

GRANT Gives other users privileges to access the

objects

CREATE ROLE Creates a collection of privileges (usually

performed by a DBA)

ALTER USER Changes a user’s password

REVOKE Removes privileges on an object from users

Embedded SQL

Embedded SQL – Most SQL statements can be embedded in host programming language such as COBOL, C, Java

int loop;

EXEC SQL BEGIN

DECLARE SECTION;

varchar

name[16],addr[30];

char eid[10];

int sal;

EXEC SQL END DECLARE

SECTION;

• SET CONNECTION

connection-name;

• DISCONNECT

connection-name;

• EXEC SQL

select NAME,ADDR,SAL

into :name,:addr,:sal

from EMPLOYEE where

EID == :eid;

Declaration of SQL variables in C SQL Database Connection in C

SQL Select Query in C

Embedded SQL for JAVA- Steps in JDBC Database Access

1. Import JDBC library (java.sql.*)

2. Load JDBC driver: Class.forname(“oracle.jdbc.driver.OracleDriv

er”)

3. Define appropriate variables

4. Create a connect object (via getConnection)

5. Create a statement object from the Statement class:

6. Identify statement parameters (designated by question marks)

7. Bound parameters to program variables

8. Execute SQL statement (referenced by an object) via JDBC’s executeQuery

9. Process query results (returned in an object of type ResultSet)

• ResultSet is a 2-dimentional table

Embedded SQL for JAVA- Example

1. import java.sql.*;

2. public class MySQLProcedure{public static void main(String[] args) {

3. try{

4. Class.forName("com.mysql.jdbc.Driver");

5. Connection c = DriverManager.getConnection("jdbc:mysql:// localhost: 3306/ db1","root", "");

6. Statement sm= c.createStatement();

7. String sql= "SELECT name, age FROM stud";

8. ResultSetrs= sm.executeQuery(sql);

9. while(rs.next()){

10. String name1 = rs.getString("name");

11. int age1 = rs.getInt(“age");

12. System.out.print(“Name age " + name1,age1);}

13. catch(Exception e){e.printStackTrace();} } }

Dynamic SQL

Sli

de 9

- 2

4

Dynamic SQL

Objective:

• Composing and executing new (not previously compiled) SQL statements at run-time

• A program accepts SQL statements from the keyboard at run-time

Dynamic query can be complex

• Because the type and number of retrieved attributes are unknown at compile time

Dynamic SQL: An Example in C

EXEC SQL BEGIN DECLARE SECTION;

varchar s1[256];

EXEC SQL END DECLARE SECTION;

prompt (“Enter command“, s1);

EXEC SQL PREPARE s2 FROM :s1;

EXEC SQL EXECUTE s2;