Introduction to DBMS
A database management system (DBMS) consists of an interrelated data
and a set of programs to access that data. The collection of data is usually
referred to as database. The primary goal of a database is to provide an
environment that is both convenient and efficient to use in retrieving and
storing database information.
Database systems are designed to manage large bodies of
information. The management of data involves both the definition of
structures for the storage of information and provision of mechanisms for the
manipulation of information. In addition, the database system must provide
for the safety of the information stored, despite system crashes or attempts
at unauthorized access. If data is stored among several users, the system
must avoid possible anomalous results.
Database systems overcomes the problems faced in file-oriented
system. The database system are controlled by the Database Administrator
(DBA)
Advantages of DBMS:
 Reduces Data redundancy (duplicity) and inconsistency of data.
 Provides data sharing facilities.
 Provides Data Integrity and Security.
 Provides Data Independence.
 Resolves concurrent access anomalies.
DATA ABSTRACTION:
A database management system provides users with an abstract view
of data, i.e. the system hides certain details of how the data is stored and
maintained. This concern has lead to the design of complex data structures
for the representation of data in the database. Its complexity is hidden from
the users through several levels of abstraction in order to simplify the
interaction between the user and the system.
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Physical Level:
The lowest level of abstraction describes the data is actually stored in
the database.
Conceptual Level:
The next-higher level of abstraction describes what data are
actually stored in the database and the relationship that exists between
them. This level is used by DBA, who must decide what information is to be
kept in the database.
View Level:
The highest level of abstraction describes only a part of the entire
database.
DATA MODELS:
A data model can be defined as a collection of tools for
describing data and the relationship between them.Data models can be
classified into the following groups.
 Object oriented logical models.
 Record based logical models.
 Physical data models.
Object oriented logical models:
They are used in describing data at the conceptual and view levels.
Some of the widely known models are
 Entity Relationship model(ER model): is based on real world
perception which consists of collection of basic objects called
‘Entities’ and ‘relationships’ among these objects.
 Object oriented model: is based on collection of objects. An
object contains instance variables within the object. An object
also contains bodies of code that operate on the object, called
methods.
Record based logical models:
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They are used in describing data at the conceptual and view levels. As the
database is structured in fixed-format records of several types, they are
called as record based logical models.
Some of the widely known models are:

Relational model: represents data and relationships among data
by a collection of tables, each of which has a number of columns with
unique names.
 Network model: represents data by collection of records and
relationships among data are represented by links which are viewed as
pointers.
 Hierarchical model: represents data by collection of records, which
are organized as trees rather than arbitrary graphs and relationships
among data are represented by links which are viewed as pointers.
 Physical models: They are used in describing data at the lowest level.
DATABASE FACILITIES:
Two main types of facilities are provided by a DBMS:
 Data definition facility or Data definition language (DDL).
 Data manipulation or Data manipulation language (DML).
Data definition language (DDL):
A database scheme is specified by a set of definitions which are
expressed by a special language called Data definition language
(DDL).The result of compilation of DDL statements is a set of tables which
are stored in a special file called Data Dictionary.
The storage structures and access methods used by the
database system are specified by a set of definitions in a special type of
DDL called Data storage and definition language. The result of
compilation of these definitions is a set of instructions to specify the
implementation details of the database schemes which are usually hidden
from others.
Data manipulation language (DML):
A Data manipulation language (DML) is a language that
enables users to access or manipulate data efficiently.
Data manipulation means
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1. Retrieval of information stored in the database.
2. Insertion of new information into the database.
3. Deletion of information from the database.
4. Modification of data stored in the database.
There two types of DMLS:
1. Procedural DMLs requires a user to specify what data is
need and how it get it.
2. Non Procedural DMLs requires a user to specify what data
is needed without specifying how to get it.
Query is a statement requesting the retrieval of information. A
portion of a DML that involves retrieval is called query
language.
STRUCTURE OF A DBMS:
The major components of this system are
Data definition language compiler:
The DDL compiler converts data definition statements into
a set of tables. These tables contain metadata concerning the database.
Data Manager:
The data manager is the central software component of the
DBMS.Its function is to convert operation queries coming from query
processor or indirectly or an application program from the user’s logical view
to physical file system. The data manager is responsible for interfacing the
file system.
File Manager:
It is responsible for the structure of files and managing the file space
and also for locating the block containing required record, requesting this
block from the disk manager, and transmitting the required record to the data
manager.
Disk manager:
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The disk manager transfers the block containing the data requested by the
file manager without the concern of physical characteristics of the underlying
storage media.
Query Processor:
The query processor is used to interpret the online user’s query and covert it
into an efficient series of operations in a form capable of being sent to the
data manager for execution. It uses data dictionary to find the structure of
the relevant portion of the database and uses this information in modifying
the query.
Data Files:
Data files contain data portion of the database.
Data Dictionary:
A data dictionary is a file that contains metadata. i.e. data about data. This
file is consulted before actual data is read or deleted in the database system.
Different types of Keys:
Attribute: An object or an entity is characterized by its properties or
attributes, they can also be referred as field.
1. Primary key: An attribute to identify a record uniquely without allowing
any null values to be entered into it is called Primary key.
Ex: empno attribute in the employee table and deptno attribute in dept table.
2. Foreign key: An attribute which is a primary key in its own table and
is used as a reference in another table is called foreign key.
3. Super Key: A primary key with a combination of other attributes for
unique identification is called super key. In other words primary key is
a minimum super key.
Ex: Empno along with ename is super key.
4. Candidate Key: The super key for which no proper subset is a super
key such a minimal super key is a candidate key.
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Ex: Ename is a candidate key.
STRUCTURED QUERY LANGUAGE(SQL)
SQL is the official standard language used to access data held in the
databases.
SQL organizes data as tables , indexes , views etc. SQL is the tool
for organizing , managing and retrieving data stored in the database.
SQL provides various features like portability , client-server
architecture ,dynamic data definition , multiple views of data etc.
SQL Statements:
SQL statements are divided into
1. Data Definition language(DDL)
2. Data Manipulation Language(DML)
3. Data Control Language (DCL)
4. Transaction Processing Language (TPL)
5. Data Retrieval Language (DRL)
Data Definition Language (DDL): These statements define the structure
of the database. DDL consists of create, alter and drop statements.
Data Manipulation Language (DML): These statements are basically
required to manipulate the records of the tabled consists of insert, delete,
and update statements.
Data Control Language (DCL): These statements are basically required to
control the tables among several users by giving access or by taking back
the access to the tables. DCL consists of grant and revoke statements.
Transaction control language (TCL): These statements are basically related
to various transactions like insert, delete, and update.
Data retrieval language (DRL): These statements are basically required to
retrieve the records for the table. DRL consists of select statements.
Data types in SQL:
1.Varchar2(size):
It is a variable length string with a max length of ‘size’ bytes.
2. Char (size):
It specifies a fixed length character string. Max size is 255
3. Number (n):
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It specifies integer type of data with max of n digits.
4.Number(p,s):
It specifies floating number with p as total no of digits and specifies the
number of digits to the right of decimal points.
5. Date: It specifies the date in DD-MM-YY format.
Data definition language (DDL):
Create statement: It is used to create and define a table.
Syntax:
Create table <table name>
(<field-name1> <data type> [column constraints],
<field-name2> <data type> [column constraints],
.
.
.
<field-name n> <data type> [column constraints]) ;
Column constraints :
1. Primary Key: It will not allow null and duplicate values corresponding to
that column.
2. Not Null : It will allow null values corresponding to that column
3. Unique: It will not allow duplicate values corresponding to that column.
4. Check: It will impose the constraints based on the condition being
mentioned on the column.
5. Reference( foreign key): It will impose the constraints based on the
condition being mentioned on the column
6. Reference (foreign key): It will refer to other column values that are
acting as primary key in other table.
7. On delete cascade: It will delete the values in the column in one table,
corresponding values in other table will be deleted automatically, and it
will work only references only.
Example 1:
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Create a table employee with employee no as primary key, name
field not be left empty, salary greater than 2000,job field not to be left
empty,deptno is foreign key taken from dept table.
Example 2:
Create dept table with deptno as primary key and dept
name as not null.
SQL>Create table Dept
(Deptno number(3) primary key,
Dname varchar2(10) not null);
Example 3: Create a customer table.
SQL>Create table Customer
(Cust_id number(5) primary key,
First_name varcahr2(20) not null,
Last_name varchar2(20) not null,
Address varchar2(40),
City varchar2(20),
State varchar2(20),
Phone_no number(9) unique);
Table Level Constraints:
Imposing constraints after declaring all the columns of the table, then
we call it as table level constraints.
Example 4: Create project table.
SQL>Create table Project
(Emp_id number(5),
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Proj_id number(5),
Payment number(8),
Primary key(Emp_id,Proj_id);
Create with Select:
To create a table from taking the records from existing table. When creating
a table based on existing table then it is going to transfer only not null
constraint, other constraints will not be transferred.
Example 1:
SQL>Create table Emp
As select Empno, Ename, Salary from Employee;
Create with select using where clause:
Example 2: Create a table empno containing the details in deptno 10 only
SQL>Create table Empd
As select * from Employee
Where deptno=10;
Alter Statement: It is used to alter the definition of a table in the database
Syntax:
Alter table<table_name>
Add
column_name data_type <column_constraint>
[Modify
column_name data_type <column_constraint>];
Add: is used when ever you want to add a new column to the table.
Example 1: Adding Phno as a new field into Employee table
SQL>Alter table Employee
Add(Phno number(7));
Example 2: Adding empno as primary key to Emp table
SQL>Alter table Emp
Add(Primary key(empno));
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Modify: is used to change the size of the column of the same data
type.Modify will not decrease the column size.Whenever it comes to increase
in the size of column it is going to allow only when the field is empty.
Example 1:
Modify the salary field by increasing its size.
SQL>Alter table Emp
Modify(sal number(9,2));
Droping the Constraints:
Example1:
Dropping Primary key constraint we must see that no references
are there from other tables.
SQL>Alter table Emp
Drop Primary key;
Drop command: is used to drop the table.
Syntax:
Drop table<table_name>;
Example 1: Dropping emp table.
SQL>Drop table emp;
Describe command: is used to display the structure of the table.Desc can
also be used
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Data Manipulation Language (DML):
Insert command: is used to add rows(or records) to the table. The number
and sequence should match that of columns in the table.If the number of
data values is less, then specify the column names into which data is being
entered. To insert null values, NULL can be used.
Syntax:
Insert into<table_name>values(datavalue_1,………..,datavalue_n);
Insert into<table_name>(column_1,column_3)
Values(datavalue_1,datavalue_3);
Example 1:
Insert 100th record into employee table.
SQL>insert into employee
Values(100,’James’,6000,’17-Mar-03’);
Example 2: Inserting 101th record into employee table with salary and date
Of joining as null values.
SQL>Insert into employee
Values(101,’James’,null,null);
Example 3: Inserting 1001th record into employee table with only empno
and name.
SQL>Insert into employee(empno,ename)
Values(1001,’John’);
Insert with select: is used to transfer the data from one table to another
table.
Syntax:
Insert into<table_name>
Select <field_name_1>,……<field_name_n> from <table_name>
Where<condition>;
Example 1:
SQL>Insert into emp
Select empno,ename,sal from employee
Where deptno=10;
Delete Command: is used to delete the records from the specified table.
Syntax:
Delete <table_name>
Where<condition>;
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Example 1: Deleting the employee holding empno1001
SQL> Delete employee where empno = 1001;
Example 2 : Delete all the records of the employee table
SQL> Delete employee;
Example 3: Delete the employees who are working as clerks.
SQL> Delete employee where job =’clerk’
Update command: is used to modify the records of the table
Syntax:
Update <table_name>
Set <field_name> = <value> ,
.
.
.
Where <condition> ;
Example1: Increase all the employees salary by Rs. 500
SQL> update employee set sal=sal+500;
Example2: Give an increment of 20% salary and commission by 5%of
salary
SQL> update employee set sal = sal* 1.2, comm = (sal* 0.05) +comm;
Example3: Promote the manager as director of the company
SQL> update employee set job =’director ‘ where job= ‘manager’;
Example4: Give an increment of 10% salary whose salary is less than Rs.
1000
SQL> update employee set sal = sal*1.1 where sal <1000;
Transaction control language(TCL);
The DML transactions will not be saved implicitly based on the following
reasons.
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1. Improper shut down
2. System crash
3. When working under SQL environment DML transactions will not
saved.
To handle DML transactions explicitly we require a set of commands which
are commit, roll back and save point.
Commit command: is used to save all the transactions up to the last
command explicitly.
SQL> insert into employee( empno, ename) values (200, ‘smith’);
SQL> commit ;
Roll back command: is used to undo the transactions up to the last
commit.
SQL> Rollback;
Savepoint: is used to minimize roll back only to certain transactions
Example:
SQL> insert ………
SQL> savepoint ins;
SQL> update …….
SQL> savepoint upd
SQL> delete ….
SQL> savepoint del;
SQL> Rollback;
SQL> commit;
SQL> Rollback to del;(Once you commit and then give rollback, will
remove all save points)
Autocommit command: is used to make all DML transactions to save
implicitly after the execution of the command.
SQL> set autocommit on;
SQL> set autocommit off;
To see the status of autocommit we use show command.
SQL> show autocommit;
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Data Retrieval language(DRL);
Select command: is used to retrieve the records from the table.
Syntax:
Select < field_name_1>, …….. , <field_name_n> from <table_name>
where <condition> ;
Example 1: To display the deptno,dname,loc.
Example 2: To display all the employee details,who are working as
manager.
SQL>Select * from emp where job-‘manager’;
Logical Operators:
 And
 Or
 Not
Example 1: To display the employee information who are working in deptno
10 and salary greater than 2000.
SQL>select * from emp
Where deptno=10 and sal>2000;
Example 2: To display the employee information who are working as
manager corresponding to deptno 20.
SQL>select * from emp
Where job=’manager’ and depno=20;
Example 3: To display the employee information who are working in deptno
10,20.
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SQL>select * from emp
Where deptno=10 or dept=20;
Example 4: To display the employee information who are working as
managers corresponding to deptno 10 as well as the employees who are
receiving salary more than 2000 corresponding to deptno 20.
SQL>select * from emp
Where job=’manager’ and deptno=10;
Special Operators:




Is null
In
Between
like
 is null: is used to check the null values corresponding to
the column.
Example 1: To display the employee information who are not receiving any
commission.
SQL>select * from emp
Where comm Is null;
 Between: Whenever we want to frame the condition in the range of
values then we use the between operator.
Example1: To display the employee information whose salary is greater than
1000 and less than 2000.
SQL>select * from emp
Where sal between 1000 and 2000;
Example 2: To display the employee information for those who are working
for deptno 10 with their first alphabet of the name is coming in the range of
‘e’ to ‘j’.
SQL>select * from emp
Where deptno=10 and(ename between ‘E’ and ‘J’);
 In: When you have multiple conditions among which any one has to
be
selected we use in operator.
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Example 1: To display the employee details who are working as managers
,clerks ,analyst.
SQL>select * from emp
Where job in(‘manager’,’clerk’,’analyst’);
Example 2:To display the employee who are working in the deptno 10,20,30.
SQL>select * from emp
Where deptno in (10,20,30);
 Like: is used when you want to frame a condition based on a particular
pattern, for which we need wild card characters, which are ‘%’ and ‘_’.
‘%’ is used to replace any no.of characters in the pattern.
‘_’ is used to replace only single characters in the pattern.
Example 1: To display the employee details whose names are ending with
‘s’.
SQL>select * from emp
Where ename like’%s’;
Example 2: To diplay the employee names have onlay 5 characters.
SQL>select * from emp
Where ename like’_____’;
Example 3: To display the employee details whose name has ‘a’ as second
character and ‘r’ as last character.
SQL>select * from emp
Where ename like’_a%r’;
Special operators with not:
Example1: To display the employee information who are receiving any
commission.
SQL>select * from emp
Where comm. Is not null;
Example 2:To display employee information for whose who are working as
managers and receiving salary other than the range 2000 to 3000.
SQL>select * from emp
Where job=’manager’ and sal not between 2000 and 3000;
Example 3:To display the employee details who are working in dept other
than 20,30.
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SQL>select * from emp
Where deptno not in (20,30);
Example 4:To display the employee details who are working in deptno 10,20
for their names not ending with ‘s’.
SQL>select * from emp
Where deptno in(10,20) and ename not like ‘%s’;
In built functions: Are classified into five types
o
o
o
o
Number Functions
Character Functions
Date functions
Group functions
Group Functions:
1. Sum(expr)
4.count(*)
2. avg(expr)
5. Max(expr)
3. count(expr)
6. min(expr)
1. Sum(expr): Is used to find total sum of the attribute or field mentioned.
Example 1: Find the sum of total salary being paid to all the employees of
the organizations.
SQL>select sum(sal) from emp;
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Example 2: Find the sum of salary and commission paid to the employees
of deptno 10.
SQL>select sum(sal+comm.) from emp
Where deptno=10;
2. avg(expr): Is used to find the average of the attribute being
mentioned.
Example: Find the average amount salary being paid to each employee.
SQL>select avg(sal) from emp;
3.Count(*): Is used to count the no.of records in the table,where the
empty record is also counted.
Example 1: find the no.of employees working in the organization.
SQL>select count(*) from emp;
Example 2:find the no.of employees working as managers and clerks in
the organization.
SQL>select count(*) from emp
Where job in(‘manager’,’clerk’);
4.count(expr): Is used to count the no.of records will the expr is satisfied.If
a record has a null value it will not count that record.
Example 1: Find the no.of employees who are receiving the commission.
SQL>select count(comm.) from emp;
Example 2: Find the no.of employees who are receiving the commission
corresponding to deptno.10,20.
SQL>select count(comm) from emp
Where deptno=10 or deptno=20;
5.max(expr): Is used to find the maximum value for the mentioned
numerical attribute.
Example 1: Find the employees who is paid the highest salary.
SQL>select max(sal) from emp;
6.min(expr): Is used to find the minimum value for the mentioned numerical
attribute.
Example: find the employees who is paid the least salary.
SQL>select min(sal) from emp;
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Numerical Functions:




abs(n)
sqrt(n)
power(n)
mod(n)
1.abs(n): Is used to find the absolute value of n.dual is dummy table for
Temporary manipulation.
SQL>select abs(-5) from dual;
2.sqrt(n): Is used to find the square root of n.
SQL>select sqrt(36) from dual;
3.power(n): Is used to find the value of m to the power of n.
SQL>select power(3,2) from dual;
4.mod(m,n): Is used to find the remainder after dividing m by n.
SQL>select mod(5,2) from dual;
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CHARACTER FUNCTIONS:





Length(str)
Concate(str1,str2)
Substr(str,pos,n)
Ascii(char)
Chr(n)
1. length(str): Returns the length of the string mentioned.
SQL>select length(‘student’) from dual;
2. concat(str1,str2): Joints string1 and string2 ot form a new string.
SQL>select concat(‘aaaa’,’bbbb’) from dual;
3. substr(str,pos,n): Returns the substring from the string from position
pos cut n characters.
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SQL>select substr(‘student’,3,4) from dual;
4. ascii(char): Returns the ascii value of the mentioned character.
SQL>select ascii(‘a’) from dual;
5.chr(n): Returns the character for the ascii value n mentioned.
SQL>select chr(68) from dual;
6.lower(str): Converts the given string into lower case.
SQL>select lower(‘AAAA’) from dual;
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8. upper(str): Converts the given string into upper case.
SQL>select upper(‘dddd’) from dual;
DATE FUNCTIONS:
1. add months(date,n): To add or remove given n months to the given
data.Sysdate gives the system date.
SQL>select sysdate from dual;
SQL>select add_month(sysdate,3) from dual;
2. months between(date1,date2): Returns the no.of months between the
two dates mentioned.Date1 is maximum value and date2 is minimum
value.The output of this function is either float or integer value.
SQL>select months_between(’29-oct-03’,’29-apr-03’) from
dual;
3. Last day(date): Returns the last day in the month specified by the date
mentioned.
SQL>select last_day(sysdate) from dual;
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Group by clause: Is used to group a set of repeated values corresponding
to a particular column for which we want to apply group function.
Example 1: To display the deptno. And total salary in each dept.
SQL>select deptno,sum(sal) from emp
Group by deptno;
Example 2: To display the dept’s highest,lowest salary and no.of
employees in each dept.
SQL>select deptno,max(sal),min(sal),count(*) from
emp group by deptno;
Example 3: To display the no.of employees receiving commission
corresponding to deptno 10,20 with their deptno.
SQL>select deptno,count(comm.) from
Emp where deptno=10 or deptno=20
Group by deptno;
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Having Clause: Is used when we want to frame the condition of salary is
greater than cannot be used with where clause.
Example 1: To display the deptno.s for which total amount of salary is
greater than 10,000.
SQL>select deptno,sum(sal) from emp
Group by deptno
Having sum(sal)>10000;
Example 2: To display the deptno.s along with their total salary for which
total salary is greater than 10,000 corresponding to deptno 10,20.
SQL>select deptno,sum(sal) from emp
Where deptno in (10,20)
Group by deptno
Having sum(sal)>10000;
Example 3 : To display the job’s along with the no.of employees working
,provided the highest salary corresponding to the job is greater than 3000
as well as the no.of employees working is more than 3.
SQL>select job,count(*) from emp
Where deptno in (10,20,30)
Group by job
Having max(sal)>2000 and count(*)>2;
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Order by clause: Is used when we want to display the data in a sorted
order.
1. Ascending order |asc| (default ordering)
2. Descending |desc|
Example 1: To display the employee information in the ascending order
of the empno.
SQL> select * from emp
Oreder by empno;
Example 2: To display the employee information in the descending order
of the salary.
SQL>select * from emp
Order by sal desc;
Example 3: To display the employee information in the ascending order
of the deptno,descending order of salary.
SQL>select * from emp
Order by deptno,sal desc;
Example 4: To display the depts along with their total payment
corresponding to deptno 10,20,30 for which n0.of employees are working
is more than 2 and display based on the descending order of total salary.
SQL>select deptno,sum(sal) from emp
Where deptno in (10,20,30)
Group by deptno
Having count(*)>2
Order by sum(sal) desc;
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SET OPERATORS:
 Union
 Intersection
 Minus
1. union: Is used to take distinct rows from more than one select
statement.By using union all the duplication is not removed.
Example 1: To display in deptno the job’s. 10 or 20.
SQL>select job from emp
Where deptno=10
Union
Select job from emp
Where deptno=20;
Example 2: To display the job’s from emp.
SQL>select job from emp
Where deptno=10
Union all
Select job from emp
Where deptno=20;
2.intersect: Is used to take common rows from more than one select
statement.
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Example 1: To dispalyb the job’s in deptno. 10 and 20.
SQL>select job from emp
Where deptno=10
Intersect
Select job from emp
Where deptno=20;
Example 2:To disaply the job’s in deptno. 10 and (20 or 30).
SQL>select job from emp
Where deptno=10
Intersect
(select job from emp
Where deptno=20
Union
Select job from emp
Where deptno=30);
2. minus: Is used to select the rows from more than first select statement
which are not in the second statement.
Example 1: To display the job’s in deptno.10 and not in 20.
SQL>select job from emp
Where deptno=10
Minus
Select job from emp
Where deptno=20;
Example 2: To list the jobs which are unique to dept 10 as compare to 20
and 30.
SQL>(select job from emp
Where deptno=20
Union
Select job from emp
Where deptno=30)
Minus
(select job from emp
Where deptno=10);
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SUB QUERIES: when we are using more than one select statement to
perform particular operation then we will be calling it as a subquery.In
subquery the inner statement will be executed first and only noce as
compared to the outer statement.
Syntax:
select ----------From<table name>
Where(select ------);
Example 1: To display all the employee’s information whose salary is
greater than Smith’s salary.
SQL>select * from emp
Where sal>(select sal from emp
Where ename=’SMITH’);
Example 2: To display all the employee’s information who is receiving the
highest salary.
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SQL>select * from employee
Where sal=(select max(sal) from emp);
Example 3: To display all the employee’s information whose job is same
like Smith at the same time salary greater than Allen.
SQL>select * from emp
Where job=(select job from emp where
ename=’SMITH’)
And sal>(select sal from emp
Where ename=’ALLEN’);
Example 4:To display all the employee’s information who is receiving salary
greater than average salary of all the employee’s.
SQL>select * from emp
Where sal>(select avg(sal) from emp);
Example 5:To display the manager no.alng with the no.of employee’s
working under him should be maximum no.of employees compared with the
other members.
SQL>select mgr,count(*) from emp
Group by mgr
Having count(*)=(select max(count(*) from
Emp group by mgr);
Example 6: To display the employee information under which maximum
no.of employee’s working.
SQL>select * from emp
Where empno=(select mgr from emp
Group by mgr)
Having count(*)=(select max(count(*) fom emp
group by mgr);
Example 7: To disaply all the employee’s information who is receiving the
second highest salary.
SQL>select * from emp
Where sal=(select max(sal) from emp where
Sa<(select max(sal) from emp));
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When the subquery is returning more than one value to frame the condition
we have to use all or any.
Example 8: To display the employee information whose salary is greater
than all the employees salaries of deptno 20.
SQL>select * from emp
Where sal>all(select sal from emp
Where deptno=20);
Views: Views can be defined as a virtual table because it doesn’t exist by
itself,unless you are having one or more ordinary table on which it will be
based or dependent.The table on which view is based is called as base table
of the view.It is possible to insert,update and delete the data in the view in
the same way as in the table.
Advantages of views:
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 Providing the security for the table.
 By giving limited access to your table to other users.
 Complicated queries can be generated by using views a normal
simple table creation.
Creation of view:
Syntax:
create view <view name>
As select ------ from <table name>;
Example 1: To create a view for emp table with empno,name,salary.
SQL>craerte view empview
As select empno,ename,sal from emp;
Example 2: To create a view for emp table for dept 10.
SQL>create view d10view
As select * from emp
Where deptno=10;
Insert into view:
Example 1: Insert a new record into view empview.
SQL>insert into empview
Values(101,’WILLIAM’,2000);
Viewing the contents of d10view:
Example: To display the contents of d10view.
SQL>select * from d10view;
31
Replace: Replace option is used whenever you want to over write the
existing select statement with new select statement.
Example: To create empview with empno,name,salary and deptno.
SQL>replace view empview
As select empno,ename,sal,deptno from emp;
With check option: When ever you want to restrict the user to insert thr
records which are satisfying the where condition of the view then we use
with check option.
Syntax: create view <view name>
As select-----from <table name>
Where <condition>
With check option;
Example : create a view for employee details of deptno. 20
SQL>create view d20view
As select * from emp
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Where deptno=20
With check option;
If you try to enter deptno other than 20,it will not be accepted into the view.
Sequences: Whenever you want to create a object which is going to
generate the numbers in a particular order (i.e. interval) then we will be
calling a sequence.
Syntax:
create sequence <seq.Name>
Start with <no.>
Increment by <interval>
Maxvalue <n>
Minvalue <n>
Cache
Cycle;
Whenever you want to generate the next number of the sequence then we
will be using nextval and when you want to see the current position of the
sequence we use currval.
Example:
SQL>create sequence eno
Start with 5
Increment by 1
Minvalue 5
Maxvalue 15
Cache 5
Cycle;
This is going to create a sequence with name eno starting with
5,incrementing by 1,minimum value is 5,maximum value is 15,cache is 5 and
with cycle.
Altering the sequence: whenever you want to change any options related t
To existing sequence then we will be using Alter.
Note:start with cannot be changed using Alter.
Syntax:
Example:
alter sequence <seq.name>
<options to be changed>;
SQL>alter sequence eno
Increment by 2
Minvalue 10
Maxvalue 100;
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Drop sequence: Whenever you want to drop a sequence we use drop
statement.
Syntax: drop sequence <seq.name>
Example: SQL>drop sequence eno;
INDEX: Whenever you to retrieve the records faster corresponding to one
condition then we will be using Indexing concept.
Before going to index,identify the fields which will be using
mostly in the where clause then indx on those fields.Apply index when there
are more than 500 records are present in a table.
There are 3 types of indexes Simple index, Unique index
and Concatenated index.
Syntax: SQL>create index <index name> on <table name>(<field name>);
1. Simple index: Is used when indexing is based on the column of the
table.
Example 1: SQL>create index idept on emp(deptno);
Example 2: SQL>create index iename on emp(ename):
2. Unique index: Is used when indexing is based on implementing
unique constraint along with indexing.
Example : SQL>create unique index iph on emp(phno);
3. concatenated index: Is used when indexing is based on more than
one column as a combination.
Example: SQL>create index ds on emp(deptno,sal);
Delete index: drop statement is used
Example: SQL>drop index idept;
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PL/SQL(Procedural Language using sql)
PL/SQL can be called the extension of SQL where it is going to support the
SQL statement along with the processing statement we will be calling it as
Procedural Language.
PL/SQL is divided into 3 parts
1.Declaration part: Declaring the variables.
2.Execution part: corresponding to the task all the statements are
be written here.
3.Exception part: Errors are to be handled properly.
to
DBMS output.put line(string): Is a function used to print message on the
screen.before using this function set serveroutput on.
SQL>set serveroutput on;
%type: Is used in declaring whenever we want to assign the same datatype
and size of one variable to another variable.
Example: sall emp.sal%type;/*sall is of same type&size as that of sal field in
emp table*/
Syntax:
Declare
:
/*Declaring block*/
Begin
:
/*Execution block*/
Exception
:
/*Exception block*/
End;
Example: Write a PL/SQL block which finds area of a circle.
SQL>ed area
Declare
R number(2):=10;
Pi constant number(4,3):=3.14;
A number(7,2);
Begin
A:=Pi*R*R;
DBMS_output.put_line(‘area is=’||to_char(a));
End;
/
35
SQL>@area; /* To execute the PL/SQL block*/
Example: Write a PL/SQL block which accepts the empno and if an
employee doesn’t have commission,he will get 10% of his salary as
commission.
Select <var> into <PL/SQL var>;
SQL>ed mcom
Declare
Eno number(5):=&emp
Comm1 emp1.comm%type;
Sal1 emp1.sal%type;
Begin
Select comm.,sal into comm1,sal1 from emp
Where empno=eno;
If comm1 is null then
Update emp1
Set comm.=sal*.1
Where empno=eno;
Else
DBMS_output.put_line(‘Commission is existing for’||to_char(eno));
End if;
End;
/
SQL>@mcom;
TRIGGER: Triggers are procedures that are sotored in the database not in
the complied form and implicitly fired when an event
occurs.Traditionally,triggers guarantee that when a specific operation is
performed related actions are performd.Triggers support the execution of a
Pl/SQL block when an INSERT<UPDATE,or DELETE occurances on a table
view.
Advantages of Triggers:
 Applying Complex Bussiness rules.
 Security.
 Auditing.
Syntax: Create or replace trigger <trigger name>
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Before/after insert or delete or update on <table name> for each
row.
Begin
:
:
End;
Example 1: Create a database Trigger corresponding to emp table which is
not going to allow the user to insert the employee’s salary more than 5000.
SQL>ed t1
Create or replace trigger eins
Before insert on emp for each row
Begin
If:new.sal>5000 then
Raise_application_erroe(-20001,’salary above 5000’);
End if;
End;
/
SQL>@t1
Example 2: Create a database Trigger on dept table which prevents the
user from updating the deptno or deleting a row from the dept table if
dependent rows are existing in the emp table( i.e. if there are any
employee’s belonging to that department).
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SQL>ed t2
Create or replace trigger updel
Before update or delete on dept for each row
Begin
Declare
No number(4);
If updating or deleting then
Select count(*) no from emp
Where deptno=:new.deptno;
If (no>1) then
Raise_application_erroe(-20001,’Records existing in
emp table’);
End if;
End if;
End;
/
SQL>@ t2
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/*PL/SQL program for checking if a number is prime or not*/
SQL>ed prime.sql
Declare
N number:=&n;
I number:=2;
R number(3):=0;
Begin
While(i<=n/2)
Loop
R:=mod(n,i);
If r=0 then
Exit;
End if;
I:=i
1;
End loop;
If r=1 then
Dbms_output.put_line(‘prime’);
else
dbms_output.put_line(‘not prime’);
end if;
end;
/
SQL>@ prime;
OUTPUT:
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/*PL/SQL Program for calculating telephone bill*/
SQL>create table telbill
(tno number(10),
Name char(15),
Address varchar2(15),
Prev number(5),
Present number(5),
Pay number(9,2));
SQL>insert into telbill(tno,name,address,prev,present)
values(&tno,’&name’,’&address’,&prev,&present);
Declare
Cursor t1 is select tno,prev,present from telbill order by present desc;
Tree t1%row
type;
Diff telbill.prev%type:=0;
Begin
Open t1;
Loop
Fetch t1 into trec;
Exit when t1%notfound;
Diff:=trec.present-trec.prev;
If diff between 0 and 200 then
Update telbill
Set pay=diff*0.80
Where tno=trec.tno;
40
Elsif diff between 200 and 400 then
Update telbill
Set pay=160+(diff-200)*1
Where tno=trec.tno;
Else
Update telbill
Set pay=160+200+(diff-400)*1.25
Where tno=trec.tno;
End if;
End loop;
Close t1;
End;
/
41
/*PL/SQL Program for Displaying the salesperson who has reached the
Target*/ .
SQL>create table sales1
(sno number(2),
Sname char(15),
Sbr cahr(15),
Tgt number(5));
SQL>insert into sales1
Values(&sno,’&sname’,’&sbr’,&tgt);
Declare
Cursor s1 is select * from sales1 order by sbr desc;
Srec s1%rowtype;
Begin
Open s1;
Dbms_output.put_line(‘SALES PERSON WHO HAVE REACHED THE
TARGET’);
Dbms_output.put_line(‘-----------------------------------------------‘);
Loop
Fetch s1 into srec;
Exit when s1%notfound;
If srec.tgt>=7500 then
Dbms_output.put_line(‘--------------------------------------------‘);
Dbms_output.put_line(‘sales person name=’||srec.sname);
Dbms_output.put_line(‘branch name=’||srec.sbr);
End if;
End loop;
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Close s1;
End;
/
43
/*PL/SQL program for calculating electricity bill*/
SQL>create table elect
(eno number(5),
Ename char(15),
Address varchar2(15),
Prev number(5),
Pres number(5),pay number(9,2));
SQL>insert into elect(eno,ename,address,prev,pres)
Values(&eno,’&ename’,’&address’,&prev,&pres);
Declare
Cursor e1 is select cno,prev,pres from elect order by eno desc;
Erec e1%rowtype;
Diff elect.prev%type:=0;
Begin
For erec in e1
Loop
Diff:=erec.pres-erec.prev;
If diff between 0 an 500 then
Update elect
Set pay=diff*0.80
Where cno=erec.cno;
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Elsif diff between 0 and 1000 then
Update elect
Set pay=diff*1.20
Where cno=erec.cno;
Elsif diff between 0 and 1500 then
Update elect
Set pay=diff*1.60
Where cno=erec.cno;
Elsif diff between 0 and 2000 then
Update elect
Set pay=diff*2
Where cno=erec.cno;
Else
Update elect
Set pay=diff*2.50
Where cno=erec.cno;
End if;
End loop;
End;
/
45
/*Program for displaying Multiplication table of a given number*/
Declare
Num number (2):=&no1;
Res number(2);
Begin
For I in 1…10
Loop
Res:=num*I;
Dbms_output.put_line(num||’*’||’=’||res);
End loop
End;
/
46
/*Program to check if a given no.is Perfect Square or not*/.
Declare
Num number(2):=&no;
N number(2);
Flag number(1):=0;
Begin
N:=num/2;
For I in 1…n
Loop
Ifmod(num,i)=0 and i*i=num then
Flag:=1;
Dbms_output.put_line(num||’is a perefect square’);
Exit;
End if;
End loop;
If flag=0 then
Dbms_output.put_line(num||’is not a perfect square’);
End if;
End;
/
47
/*Program to check if a given string is Palindrome or not*/
Declare
S varchar2(10):=’&str’;
Len number(2);
C char(1);
T varchar2(10);
Begin
Select length(s) into len from dual;
For i in reverse 1..len
Loop
C:=substr(s,I,1);
T:=concat(t,c);
End loop;
If s=t then
Dbms_output.put_line(s||’is a palindrome’);
Else
Dbms_output.put_line(s||’is not a palindrome’);
End if;
End;
/
48
/*Program to generate Fibonacci Series*/
SQL>create table fibo
(fs number(5));
Declare
F1 number(3):=0;
F2 number(3):=1;
F3 number(3):=0;
J number(3):=&limit;
Begin
For I in 1..j
Loop
F3:=f1+f2;
Dbms_output.put_line(to_char(f3));
Insert into fibo
Value(f3);
F1:=f2;
F2:=f3;
End loop;
End;
/
49
/*Program for generating the Pay Slip for each Employee No.given*/
Declare
I number(5):=&eno;
Cursor e is select empno,ename,sal from emp where empno=I;
No emp.empno%type;
Name emp.ename%type;
S emp.sal%type;
Da number(7,2);
Hra number(7,2);
Pf number(7,2);
Net number(7,2);
Begin
Open e;
Loop
Fetch e into no,name,s;
Exit when e%notfound;
Dbms_output.put_line(‘______________________’);
Dbms_output.put_line(‘******STAR COMPANY******’);
Dbms_output.put_line(‘*****PAY SLIP********’);
Dbms_output.put_line(‘____________________’);
Dbms_output.put_line(‘empno=’||no);
Dbms_output.put_line(‘emplyee name’||name);
Dbms_output.put_line(‘basic salary=’||s);
Da:=s&0.025;
Dbms_output.put_line(‘da=’||da);
Hra:=s*0.05;
Dbms_output.put_line(‘hra=’||hra);
Pf:=s*0.015;
Dbms_output.put_line(‘pf=’||pf);
Net:=s+da+hra-pf;
Dbms_output.put_line(‘gross salary=’||net);
End loop;
Close e;
End;
/
50
/*Program to insert in the table & display the Division of the given
Student*/
SQL>create table s
(rno number(3),
M number(3),
S number(3),
C number(3),
Div varchar(20));
Declare
R number(3):=&rollno;
M1 s.m%type;
S1 s.s%type;
C1 s.c%type;
D s.div%type;
P number(7,2):=0;
Begin
Select m,s,c into m1,s1,c1 from s where rno=r;
P:=(m1+s1+c1)/3;
If p>70 then
D:=’distinction’;
Elsif p between 60 and 70 then
D:=’first division’;
Elsif p>=50 and p<=60 then
D:=’second division’;
Elsif p>=40 and p<=50 then
D:=’third division’;
Else
D:=’fail’;
End if;
Update s
Set div=d
Where rno=r;
Dbms_output.put_line(‘result=’||d);
End;
/
51