dbms complete

8/11/2019 Dbms Complete

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Experiment 1

Aim: Describe Data Base Management System.

DBMS (Data Base Management System):Is a system or computer software that is

designed for the purpose to manage information or databases in such way so that data

storage and retrieval of information gets easy, so we can easily say that DBMS defines

what will be the structure for information storage and in addition to it facilitates in data

manipulation. The common examples of Data Base Management Systems are Microsoft

Access, DB2, Oracle, SQL Server etc. There are some common goals while using

DBMS.

(1) Security.

(2) Backup and Replication.

(3) Change and Access Logging.

(4) Automated Optimization.

(5) Policy Enforcement.

(6) Query Ability.

(7) Meta Data Repository.

(8) Computation.

There are three most commonly used database models.

(1) Hierarchal: A hierarchical database model is adata model in which the data isorganized into atree-like structure. The structure allows representing information using

parent/child relationships: each parent can have many children, but each child has only

one parent (also known as a 1-to-many relationship). All attributes of a specific record

are listed under an entity type.

(2) Network:The network structure consists of more complex relationships. Unlike the

hierarchical structure, it can relate to many records and accesses them by following one

of several paths. In other words, this structure allows for many-to-many relationships.

(3) Relational:The relational structure is the most commonly used today. It is used by

mainframe, midrange and microcomputer systems. It uses two-dimensional rows and

columns to store data. The tables of records can be connected by common key values.

The model is not easy for the end user to run queries with because it may require a

complex combination of many tables.
http://en.wikipedia.org/wiki/Data_modelhttp://en.wikipedia.org/wiki/Tree_data_structurehttp://en.wikipedia.org/wiki/Tree_data_structurehttp://en.wikipedia.org/wiki/Data_model


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Advantages of DBMS over File Processing System:

The DBMS has a number of advantages as compared to traditional computer file

processing approach.

1. Controlling Data Redundancy:In non-database systems (traditional computer file processing), each application programhas its own files. In this case, the duplicated copies of the same data are created at many

places. In DBMS, all the data of an organization is integrated into a single database. Thedata is recorded at only one place in the database and it is not duplicated. For example,

the dean's faculty file and the faculty payroll file contain several items that are identical.

When they are converted into database, the data is integrated into a single database sothat multiple copies of the same data are reduced to-single copy.

In DBMS, the data redundancy can be controlled or reduced but is not removed

completely. Sometimes, it is necessary to create duplicate copies of the same data itemsin order to relate tables with each other. By controlling the data redundancy, you can save

storage space. Similarly, it is useful for retrieving data from database using queries.

2. Data Consistency:By controlling the data redundancy, the data consistency is obtained. If a data item

appears only once, any update to its value has to be performed only once and the updatedvalue (new value of item) is immediately available to all users.

If the DBMS has reduced redundancy to a minimum level, the database system enforces

consistency. It means that when a data item appears more than once in the database and isupdated, the DBMS automatically updates each occurrence of a data item in the database.

3. Data Sharing:In DBMS, data can be shared by authorized users of the organization. The DBA manages

the data and gives rights to users to access the data. Many users can be authorized toaccess the same set of information simultaneously. The remote users can also share same

data. Similarly, the data of same database can be shared between different application

programs.

4. Data Integration:In DBMS, data in database is stored in tables. A single database contains multiple tablesand relationships can be created between tables (or associated data entities). This makes

easy to retrieve and update data.


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5. Integrity Constraints:Integrity constraints or consistency rules can be applied to database so that the correctdata can be entered into database. The constraints may be applied to data item within a

single record or they may be applied to relationships between records.

Examples:

The examples of integrity constraints are:

(i) 'Issue Date' in a library system cannot be later than the corresponding 'Return Date' ofa book.

(ii) Maximum obtained marks in a subject cannot exceed 100.

(iii) Registration number of BCS and MCS students must start with 'BCS' and 'MCS'respectively etc.

There are also some standard constraints that are intrinsic in most of the DBMSs. Theseare;

Constraint Name Description

PRIMARY KEY Designates a column or combination of columns as

Primary Key and therefore, values of columns cannot be

repeated or left blank.

FOREIGN KEY Relates one table with another table.

UNIQUE Specifies that values of a column or combination of

columns cannot be repeated.

NOT NULL Specifies that a column cannot contain empty values.CHECK Specifies a condition which each row of a table must

satisfy.

6. Data Security:Data security is the protection of the database from unauthorized users. Only the

authorized persons are allowed to access the database. Some of the users may be allowedto access only a part of database i.e., the data that is related to them or related to their

department. Mostly, the DBA or head of a department can access all the data in the

database. Some users may be permitted only to retrieve data, whereas others are allowed

to retrieve as well as to update data. The database access is controlled by the DBA. Hecreates the accounts of users and gives rights to access the database. Typically, users or

group of users are given usernames protected by passwords.

Most of the DBMSs provide the security sub-system, which the DBA uses to createaccounts of users and to specify account restrictions. The user enters his/her account

number (or username) and password to access the data from database. For example, ifyou have an account of e-mail in the "hotmail.com" (a popular website), then you have to


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and it can be modified very easily. The created reports are also saved along with database

and behave like a software component.

12. Control Over Concurrency:

In a computer file-based system, if two users are allowed to access data simultaneously, itis possible that they will interfere with each other. For example, if both users attempt to

perform update operation on the same record, then one may overwrite the values recordedby the other. Most DBMSs have sub-systems to control the concurrency so that

transactions are always recorded" with accuracy.

13. Backup and Recovery Procedures:In a computer file-based system, the user creates the backup of data regularly to protect

the valuable data from damaging due to failures to the computer system or applicationprogram. It is a time consuming method, if volume of data is large. Most of the DBMSs

provide the 'backup and recovery' sub-systems that automatically create the backup ofdata and restore data if required. For example, if the computer system fails in the middle

(or end) of an update operation of the program, the recovery sub-system isresponsible formaking sure that the database is restored to the state it was in before the program started

executing.

14. Data Independence:The separation of data structure of database from the application program that is used to

access data from database is called data independence. In DBMS, database and

application programs are separated from each other. The DBMS sits in between them.You can easily change the structure of database without modifying the application

program. For example you can modify the size or data type of a data items (fields of a

database table). On the other hand, in computer file-based system, the structure of dataitems are built into the individual application programs. Thus the data is dependent on the

data file and vice versa.

15. Advanced Capabilities:DBMS also provides advance capabilities for online access and reporting of data through

Internet. Today, most of the database systems are online. The database technology is used

in conjunction with Internet technology to access data on the web servers.

Disadvantages of Database Management System (DBMS):

Although there are many advantages but the DBMS may also have some minor

disadvantages. These are:


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1. Cost of Hardware & Software:A processor with high speed of data processing and memory of large size is required to

run the DBMS software. It means that you have to upgrade the hardware used for file-

based system. Similarly, DBMS software is also very costly.

2. Cost of Data Conversion:When a computer file-based system is replaced with a database system, the data storedinto data file must be converted to database files. It is difficult and time consuming

method to convert data of data files into database. You have to hire DBA (or databasedesigner) and system designer along with application programmers; Alternatively, you

have to take the services of some software houses. So a lot of money has to be paid fordeveloping database and related software.

3. Cost of Staff Training:Most DBMSs are often complex systems so the training for users to use the DBMS isrequired. Training is required at all levels, including programming, application

development, and database administration. The organization has to pay a lot of amounton the training of staff to run the DBMS.

4. Appointing Technical Staff:The trained technical persons such as database administrator and application

programmers etc are required to handle the DBMS. You have to pay handsome salaries to

these persons. Therefore, the system cost increases.

5. Database Failures:In most of the organizations, all data is integrated into a single database. If database is

corrupted due to power failure or it is corrupted on the storage media, then our valuable

data may be lost or whole system stops.


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Experiment 2

AIM: To create a table in SQL.

Theory:SQL stands for Structured Query Language. SQL lets you access andmanipulate databases using various commands with a particular syntax.The query and

update commands form the DML part of SQL:

SELECT - extracts data from a database

The most important DDL statements in SQL are:

CREATE DATABASE - creates a new database

CREATE TABLE - creates a new table

ALTER TABLE - modifies a table

DROP TABLE - deletes a table

SYNTAX:

Create table syntax:

CREATE TABLE table_name

(

column_name1 data_type constraint1,column_name2 data_type constraint2,

column_name3 data_type constraint3,

....)

*constraint field are optional.

View created table:

To view the table to be created we use Des command.

Desc table_name;

Project for Management of Data Base System

Library Management System:


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We have created a database that manages a library system using SQL language. The tablewith there screenshots are:

Table 1: StaffAttributes: Employ_ID, Name,Departement, DOB, Book_ID, Membership_Code


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Table 3: Books Issued

Attributes:Book_ID, Name_of_Book, Author, Semester, Date_of_issue,Admin_ID,Issuer_ID, Issuer_ID


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Table 4:BookBook_ID, Name, Author, Semester


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Table 5: Fine

Issuer_ID, Name, Book_Name, Price, Fine


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Experiment 3

AIM: To alter a created table in SQL.

Theory:Alter command is used to alter or modify the schema of the required table. Altercommand can be used for various tasks in a table some of them are:

To add an attribute inside a table. To rename an attribute inside a table.

To delete a given attribute in a table.

To alter the data type of the attribute in a table.

To rename a table.

To add a constraint (like Primary Key) to a given attribute.

To delete a constraint (like Not Null) to a given attribute.

SYNTAX:

To add an attribute inside a table.

alter table table_name

add(columnname 1 datatype1 constraint1(optional),

columnname 2 datatype2 constraint2(optional),

-------------------------------

columnname n datatypen

);

To rename an attribute inside a table.

Alter table table_name

Rename column old_name to new_name

;

To delete a given attribute in a table


Drop (attribute_name);


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To alter the data type of the attribute in a table.


Modify ( attribute_name1 new datatype1,

attribute_name2 new datatype2,

--------------------------------------

attribute_namen new datatypen

);

To rename a table


Rename to new table_name

;

To add a constraint (like Primary Key) to a given attribute.


Add (constraint constraint_label constraint name (attribute_name))

;

To delete a constraint (like Not Null) to a given attribute


Drop constraint constraint_label

;

Examples of above commands with their screen shots applied on our LibraryManagement Database are shown as follows:


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Adding an attribute price of data type number in table book.


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To rename column Date_of_birth to DOB.


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To drop an attribute price in a table book.


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To modify the data type of employee_id, book_id and membership_code to

varchar, number and number respectively.


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To change the table name Staff to Employee.


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To add a Primary Key constraint to Book_ID.


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To delete a Primary Key constraint on Book_ID.


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To rename column name name_of_books to Book_name.


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Inserting records in table Employee


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Inserting records in table Student


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Inserting records in table Book


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Inserting records in the table Book_issued


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Inserting records in table Fine


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Experiment 5

AIM: To delete records in tables created in SQL?

THEORY: Delete command is also a DML command. It is used to delete records in the

required table. While deleting a row if we need to apply a condition to it, then we have touse this command with where.

SYNTAX: There are various formats in which the delete command can be used. Some of

them are:

Delete from table_name

where condition;

Delete from table_name; //It deletes all rows from table

Examples of above commands with their screen shots applied on our LibraryManagement Database are shown in the following pages:

Deletion command applied on table student:(using where condition 4 screen shots)


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Delete command on table student(deleting complete rows)


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Experiment 6

AIM: To use group by command in table created in SQL?

THEORY:The GROUP BY statement is used in conjunction with the aggregate

functions to group the result-set by one or more columns and display it to user. SQLaggregate functions are: Sum, Min, Max, Count, Avg. To give a condition while usingthe group by function we can use the statement havingwith it.

SYNTAX:

Select aggregate function (column1)

From table_name

Group by column1;

Select aggregate function (column1)

From table_name

Group by column1

Having condition;

Examples of above commands with their screen shots applied on our LibraryManagement Database are shown in the following pages:


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Screenshot1: Here we can see that the fine attribute is added from the table fine

grouped according to the price. For example sum of fine on all the books whoseprice is 400 is 180 as shown in the output arranged in ascending order according to

the price. Here Sum is an aggregate function used.


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Screenshot2: Here we have count the number of time the fine issued on a same

price book( that is grouped by price)For example number of times the book with price 400 is fined is 3 as shown in the

output and verified by the table displayed in screenshot1.


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Screenshot3: Here I have used a having statement with group by to give a

condition inside my command. Here sum of fine will be grouped by according tothe price as in screenshot1. But the only difference here will be that the command

will be applicable only for the rows or records that have price>300 as shown in the

output.


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Screenshot4: Here we count number of books for each sem. For example for 4 sem

there are 4 books as shown in output.


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Screenshot5:Here same operation is done as in screenshot 4 but here we used a

condition by using having command with groupby.


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Experiment 7

AIM: To arrange the data in a table created in SQL?

THEORY:To arrange a data inside a table created in SQL the command used is order by.

Order by command arranges the data in table in ascending (by default) or descendingorder according to our preference.

SYNTAX:

This syntax arranges the data in ascending order by default applied on the column

column_name.

Select * from table_name

Order by column_name;

This syntax arranges the data in descending order (desc) applied on the column

column_name.

Select * from table_name

Order by column_name desc;

Examples of above commands with their screen shots are shown in the following pages:


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Screenshot1: Here the table is arranged according to book_id.


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Screenshot2: Here table is arranged according to name attribute alphabetically and

according to sem.


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Experiment 8

AIM: To modify the data in tables created in SQL?

THEORY:To modify the records inserted in table we have to use the command update.

We have to set the value of a particular column where the condition identifies theparticular tuple or row.

SYNTAX:

To make change in a single column:

Update table_name

Set column=value/expression

Where condtion;

To make change in multiple column:Update table_name

Set column1=value/expression , column2=value/expression

Where condtion;

When more than one condition is to be implemented:

Update table_name

Set column=value/expression

Where condtion1 AND condition2;

Examples of above commands with their screen shots applied on our Library

Management Database are shown in the following pages:

Screenshot1:Original Table book


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Screenshot2: Here multiple values are set.


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Screenshot3: Here we have given multiple conditions.


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Screenshot4: Here one condition is given.


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Experiment 9

AIM: To apply Join operations in tables created in SQL?

THEORY:Join operation combines records from two or moretables in a database. It

creates a set that can be saved as a table or used as it is. A JOIN is a means for combiningfields from two tables by using values common to each. There are different types of join

operation:-

Cross Join: It is also known as Cartesian product of two tables. It returns the

Cartesian product of rows from tables in the join. In other words, it will produce

rows which combine each row from the first table with each row from the second

table.

Inner Join: It is also known as Equi-Join or Simple Join operation. It isa specific

type of comparator-based join, or theta join, that uses onlyequality comparisons in

the join-predicate. Using other comparison operators (such as


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Left Outer Join

Select table1.column, table2.column

From table1, table2

Where table1.column(+)=table2.column;

ORSelect from table1 leftouterjoin table2

On table1.column=table2.column;

Right Outer Join

Select table1.column, table2.column

From table1, table2

Where table1.column=table2.column(+);

OR

Select from table1 rightouterjoin table2On table1.column=table2.column;

Full Outer Join

Select from table1 fullouterjoin table2

On table1.column=table2.column;

Self Join

Select column1, column2, cloumn3

From table1 a, table1 b

Where a.column1=b.column2;

Table Alias: In the above syntax we used a for table1 and b for table 2. This method

reduces the code length and gives the programmer a shortcut in SQL; a and b are

called the table alias and can be used inside the commands whenever required.



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SCREENSHOT1:All the Join operations will be done on the following tables

(Employee and departement). The table is shown in the screenshot along with the

tuples.

SCREENSHOT2: It describes the cross join/Cartesian product operation on the

two tables with and without condition. In one part a condition is given which

reduces the number of tuples and in second part 24 rows are selected.


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SCREENSHOT3: It describes the inner join operation.


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SCREENSHOT4: It describes the left outer join operation on the tables.

SCREENSHOT5: It describes the right outer join operation.

SCREENSHOT6: It describes full outer join operation.


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Experiment 10AIM: To insert data in a table with the help of subquery?

THEORY: Subquery or Inner query or Nested query is a query in a query. A subquery is

usually added in the WHERE Clause of the sql statement. Most of the time, a subquery isused when you know how to search for a value using a SELECT statement, but do not

know the exact value. Subqueries are an alternate way of returning data from multipletables. During execution of a subquery command in SQL, the innermost query executesfirst.

Subqueries can be used with the following sql statements along with the comparisonoperators like =, , >=, 2);

To copy schema as well as data from one table to another.

Create table as

(select * from );

To copy schema and data from one table to another with some conditions.

Create table as

(select * from where condition);



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Screenshot1: The schema of a table student1 is copied into another table student2.

Screenshot2: The schema as well as data of table student1 is copied into the table

student3.


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Screenshot3: A new table student4 is created from student1. Student4 contain data

of all the students that have se as there department.


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Experiment 11AIM: To retrieve, delete, and update the date in a table using subquery?

THEORY: Subquery or Inner query or Nested query is a query in a query. A subquery is

usually added in the WHERE Clause of the sql statement. A subquery can also be use toretrieve, delete and update the information or data in a table created in SQL.

The subqueries can be applied on same as well as on different table to get the required

results.

There are 2 types of retrieval in SQL: Single Row and Multiple Row.

When inner query returns a single tuple as its query output then its single row retrieval

else it is multiple row retrieval.

SYNTAX:

To retrieve data from a table.

Select select_list

From table

Where expression_operator

(select select_list

from table);

To delete data from the tableDelete from where

In(subquery);

To update data in a table.

Update

Set= (subquery1)

= (subquery2)

Where condition;



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Screenshot1: Here I have retrieved the data from the table student. List of all the

students are displayed except the student having mechanical department. It is an

example of multiple row retrieval of data.


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Screenshot2: This screenshot describe the single row retrieval of data from table

student1

Screenshot3: All the student having branch cse are deleted from the table student1

using a subquery.


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Screenshot4: Here I have updated the table student1 using a subquery. The name of

the student with roll no 10160 is changed to karma as displayed below.


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Experiment 12AIM: Describe PL/SQL (Procedural Language/Structured Query Language)?

PL/SQL (Procedural Language/Structured Query Language)isOracle Corporation's

procedural extensionlanguage forSQL and theOracle relational database.PL/SQL'sgeneralsyntax resembles that ofAda orPascal.PL/SQL is one of three key programming

languages embedded in the Oracle Database, along with SQL itself andJava.

PL/SQL is Oracle's procedural language extension to SQL, the relational database

language. PL/SQL fully integrates

modern software engineering features such as data encapsulation, information hiding,overloading, and exception handling, and so brings state-of-the-art programming to the

ORACLE Server and a variety of ORACLE tools

Overview of PL/SQL:With PL/SQL, you can use SQL statements to manipulate ORACLE data and flow-of-

control statements to process the data. Moreover, you can declare constants and variables,define subprograms (procedures and functions), and trap runtime errors. Thus, PL/SQL

combines the data manipulating power of SQL with the data processing power ofprocedural languages.

PL/SQL is a block-structured language. That is, the basic units (procedures, functions,and anonymous blocks) that make up a PL/SQL program are logical blocks, which can

contain any number of nested sub-blocks. Typically, each logical block corresponds to aproblem or subproblem to be solved. A block (or sub-block) lets you group logically

related declarations and statements. That way you can place declarations close to wherethey are used. The declarations are local to the block and cease to exist when the block

completes.

[DECLARE-- declarations]BEGIN

-- statements[EXCEPTION-- handlers]

END;

PL/SQL TablesPL/SQL provides two composite datatypes: TABLE and RECORD. Objects of type

TABLE are called PL/SQL tables, which are modeled as (but not the same as) database

tables. PL/SQL tables use a primary key to give you array-likeaccess to rows.
http://en.wikipedia.org/wiki/Oracle_Corporationhttp://en.wikipedia.org/wiki/Procedural_programminghttp://en.wikipedia.org/wiki/Programming_languagehttp://en.wikipedia.org/wiki/SQLhttp://en.wikipedia.org/wiki/Oracle_Databasehttp://en.wikipedia.org/wiki/Syntax_%28programming_languages%29http://en.wikipedia.org/wiki/Ada_%28programming_language%29http://en.wikipedia.org/wiki/Pascal_%28programming_language%29http://en.wikipedia.org/wiki/Java_%28programming_language%29http://en.wikipedia.org/wiki/Java_%28programming_language%29http://en.wikipedia.org/wiki/Pascal_%28programming_language%29http://en.wikipedia.org/wiki/Ada_%28programming_language%29http://en.wikipedia.org/wiki/Syntax_%28programming_languages%29http://en.wikipedia.org/wiki/Oracle_Databasehttp://en.wikipedia.org/wiki/SQLhttp://en.wikipedia.org/wiki/Programming_languagehttp://en.wikipedia.org/wiki/Procedural_programminghttp://en.wikipedia.org/wiki/Oracle_Corporation


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Like the size of a database table, the size of a PL/SQL table is unconstrained. That is, the

number of rows in a PL/SQL table can increase dynamically. The PL/SQL table grows asnew rows are added.

PL/SQL tables can have one column and a primary key, neither of which can be named.

The column can belong to any scalar type, but the primary key must belong to typeBINARY_INTEGER.

Interaction With ORACLE:

SQL SupportBy extending SQL, PL/SQL offers a unique combination of power and ease of use. You

can manipulate ORACLE data flexibly and safely because PL/SQL supports all SQL data

manipulation commands (except EXPLAIN PLAN), transaction control commands,functions, pseudocolumns, and operators. However, PL/SQL does not support data

definition commands such as CREATE, session control commands such as SET ROLES,

or the system control command ALTER SYSTEM.

Data Manipulation

To manipulate ORACLE data, you use the INSERT, UPDATE, DELETE, SELECT, and

LOCK TABLE commands.

Transaction Control

ORACLE is transaction oriented; that is, ORACLE uses transactions to ensure dataintegrity. A transaction is a series of SQL data manipulation statements that does a

logical unit of work. For example, two UPDATE statements might

credit one bank account and debit another. At the same instant, ORACLE makespermanent or undoes all database changes made by a transaction. If your program fails in

the middle of a transaction, ORACLE detects the error and rolls back the transaction.Hence, the database is restored to its former state automatically.

You use the COMMIT, ROLLBACK, SAVEPOINT, and SET TRANSACTION

commands to control transactions.COMMIT makes permanent any database changes made during the current transaction.

Until you commit your changes, other users cannot see them. ROLLBACK ends the

current transaction and undoes any changes made since the transaction began.SAVEPOINT marks the current point in the processing of a transaction. Used with

ROLLBACK, undoes part of a transaction. SET TRANSACTION establishes a read-only

transaction


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CONTROL STRUCTURES

According to the structure theorem, any computer program can be written using the basiccontrol structures which can be combined in any way necessary to deal with a given

problem.

The selection structure tests a condition, then executes one sequence of statementsinstead of another, depending on whether the condition is true or false. A condition is any

variable or expression that returns a Boolean value (TRUE, FALSE, or NULL). Theiteration structure executes a sequence of statements repeatedly as long as a condition

holds true. The sequence structure simply executes a sequence of statements in the orderin which they occur.

Conditional Control: IF Statements

Often, it is necessary to take alternative actions depending on circumstances. The IFstatement lets you execute a sequence of statements conditionally. That is, whether the

sequence is executed or not depends on the value of a

condition. There are three forms of IF statements: IF-THEN, IF-THEN-ELSE, and IF-THEN-ELSIF.The third form of IF statement uses the keyword ELSIF (NOT ELSEIF) to introduce

additional conditions, as follows:

IF condition1 THENsequence_of_statements1;

ELSIF condition2 THEN

sequence_of_statements2;ELSE

sequence_of_statements3;

15END IF;

Iterative Control: LOOP and EXIT Statements

LOOP statements let you execute a sequence of statements multiple times. There are

three forms of LOOP statements:

LOOP, WHILE-LOOP, and FOR-LOOP.

LOOPThe simplest form of LOOP statement is the basic (or infinite) loop, which encloses a

sequence of statements between

the keywords LOOP and END LOOP, as follows:LOOP

sequence_of_statements3;

...END LOOP;


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With each iteration of the loop, the sequence of statements is executed, then control

resumes at the top of the loop. If further processing is undesirable or impossible, you canuse the EXIT statement to complete the loop. You can place

one or more EXIT statements anywhere inside a loop, but nowhere outside a loop. There

are two forms of EXIT statements: EXIT and EXIT-WHEN.The EXIT statement forces a loop to complete unconditionally. When an EXIT statement

is encountered, the loop completes immediately and control passes to the next statement.LOOP

...IF ... THEN

...

EXIT; -- exit loop immediatelyEND IF;

END LOOP;

-- control resumes hereThe EXIT-WHEN statement allows a loop to complete conditionally. When the EXITstatement is encountered, the condition in the WHEN clause is evaluated. If the condition

evaluates to TRUE, the loop completes and control passes to the next statement after the

loop.LOOP

FETCH c1 INTO ...

EXIT WHEN c1%NOTFOUND; -- exit loop if condition is true...

END LOOP;

CLOSE c1;Until the condition evaluates to TRUE, the loop cannot complete. So, statements within

the loop must change the valueof the condition.

Like PL/SQL blocks, loops can be labeled. The label, an undeclared identifier enclosed

by double angle brackets, must

appear at the beginning of the LOOP statement, as follows:

LOOP

sequence_of_statements;...

16

END LOOP [label_name];Optionally, the label name can also appear at the end of the LOOP statement.


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With either form of EXIT statement, you can complete not only the current loop, but any

enclosing loop. Simply label the enclosing loop that you want to complete, then use thelabel in an EXIT statement.

LOOP...

LOOP...

EXIT outer WHEN ... -- exit both loopsEND LOOP;

...

END LOOP outer;

WHILE-LOOP

The WHILE-LOOP statement associates a condition with a sequence of statements

enclosed by the keywords LOOP and END LOOP, as follows:WHILE condition LOOPsequence_of_statements;

...

END LOOP;Before each iteration of the loop, the condition is evaluated. If the condition evaluates to

TRUE, the sequence of statements is executed, then control resumes at the top of the

loop. If the condition evaluates to FALSE or NULL, the loop is bypassed and controlpasses to the next statement. Since the condition is tested at the top of the loop, the

sequence might execute zero times.

FOR-LOOP

Whereas the number of iteration through a WHILE loop is unknown until the loop

completes, the number of iterations through a FOR loop is known before the loop isentered. FOR loops iterate over a specified range of integers. The range is part of an

iteration scheme, which is enclosed by the keywords FOR and LOOPS.

FOR counter IN [REVERSE] lower_bound..upper_bound LOOP

sequence_of_statements;...

END LOOP;

The lower bound need not be 1. However, the loop counter increment (or decrement)must be 1.

PL/SQL lets you determine the loop range dynamically at run time, as the following

example shows:SELECT COUNT(empno) INTO emp_count FROM emp;

FOR i IN 1..emp_count LOOP...


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END LOOP;

17The loop counter is defined only within the loop. You cannot reference it outside the

loop. You need not explicitly

declare the loop counter because it is implicitly declared as a local variable of typeINTEGER.

The EXIT statement allows a FOR loop to complete prematurely. You can complete notonly the current loop, but any

enclosing loop.

dbms complete

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