sql.pdf

Computer Science
Class XII ( As per CBSE Board)
Chapter 11
Structured
Query
Language
New
syllabus
2020-21
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SQL
SQL is an acronym of Structured Query Language.It is a
standard language developed and used for accessing and
modifying relational databases.
The SQL language was originally developed at the IBM research
laboratory in San José, in connection with a project developing
a prototype for a relational database management system
called System R in the early 70s.
SQL is being used by many database management systems.
Some of them are:
MySQL
PostgreSQL
Oracle
SQLite
Microsoft SQL Server

Advantages of using SQL
 Interactive Language-This language can be used for
communicating with the databases and receive answers to the
complex questions in seconds.
 Multiple data views-The users can make different views of
database structure and databases for the different users.
 Portability-SQL can be used in the program in PCs, servers,
laptops, and even some of the mobile phones and even on
different dbms softwares
 No coding needed-It is very easy to manage the database
systems without any need to write the substantial amount of
code by using the standard SQL.
 Well defined standards-Long established are used by the SQL
databases that is being used by ISO and ANSI. There are no
standards adhered by the non-SQL databases.
SQL

MySQL is currently the most popular open source
database software. It is a multi-user, multithreaded
database management system. MySQL is especially
popular on the web. It is one of the parts of the very
popular LAMP platform. Linux, Apache, MySQL and PHP
or WIMP platform Windows,Apache,MySQL and PHP.
MySQL AB was founded by Michael Widenius (Monty),
David Axmark and Allan Larsson in Sweden in year 1995.
SQL

MySQL Features
Open Source & Free of Cost:
It is Open Source and available at free of cost.
 Portability:
Small enough in size to instal and run it on any types of Hardware and
OS like Linux,MS Windows or Mac etc.
 Security :
Its Databases are secured & protected with password.
 Connectivity
Various APIs are developed to connect it with many programming
languages.
 Query Language
It supports SQL (Structured Query Language) for handling database.
SQL

Types of SQL Commands
 DDL (Data Definition Language)
To create database and table structure-commands
like CREATE , ALTER , DROP etc.
 DML (Data Manipulation Language)
Record/rows related operations.commands like
SELECT...., INSERT..., DELETE..., UPDATE.... etc.
 DCL (Data Control Language)
used to manipulate permissions or access rights to the
tables. commands like GRANT , REVOKE etc.
 Transactional control Language.
Used to control the transactions.commands like
COMMIT, ROLLBACK, SAVEPOINT etc.
SQL

Data type in MySQL
 Numeric Data Types:
 INTEGER or INT – up to 11 digit number without decimal.
 SMALLINT – up to 5 digit number without decimal.
 FLOAT (M,D) or DECIMAL(M,D) or NUMERIC(M,D)
Stores Real numbers upto M digit length (including .) with D
decimal places.
e.g. Float (10,2) can store 1234567.89
 Date & Time Data Types:
 DATE - Stores date in YYYY-MM-DD format.
 TIME - Stores time in HH:MM:SS format.
 String or Text Data Type:
 CHAR(Size)
A fixed length string up to 255 characters. (default is 1)
 VARCHAR(Size)
A variable length string up to 255 characters.
Char, Varchar, Date and Time values should be enclosed with single (‘ ‘) or double (
“”) quotes in MySQL. varchar is used in MySQL and varchar2 is used in Oracle.
SQL

Database Commands in MySql
Getting listings of available databases
mysql> SHOW DATABASES;
Creating a database-
mysql> CREATE database myschool;
Deleting a database mysql> DROP database <databasename>;
to remove table mysql> drop table <tablename>;
After database creation we can open the database using USE command
mysql> USE myschool;
To show list of tables in opened database
mysql> SHOW TABLES;
Creating a table in the database is achieved with CREATE table statement.
mysql> CREATE TABLE student (lastname varchar(15),firstname varchar(15), city
varchar(20), class char(2));
The command DESCRIBE is used to view the structure of a table.
mysql> DESCRIBE student;
SQL

To insert new rows into an existing table use the INSERT command:
mysql>INSERT INTO student values(‘dwivedi’,’freya’,’Udaipur’,’4’);
We can insert record with specific column only
mysql>INSERT INTO student(lastname,firstname,city) values(‘dwivedi’,’Mohak’,’Udaipur’,);
With the SELECT command we can retrieve previously inserted rows:
A general form of SELECT is:
SELECT what to select(field name) FROM table(s)
WHERE condition that the data must satisfy;
• Comparison operators are: < ; <= ; = ; != or <> ; >= ; >
• Logical operators are: AND ; OR ; NOT
• Comparison operator for special value NULL: IS
mysql> SELECT * FROM student;
SQL

Selecting rows by using the WHERE clause in the SELECT command
mysql> SELECT * FROM student WHERE class=“4";
Selecting specific columns(Projection) by listing their names
mysql> SELECT first_name, class FROM student;
Selecting rows with null values in specific column
mysql> SELECT * FROM Student WHERE City IS NULL ;
 BETWEEN- to access data in specified range
mysql> SELECT * FROM Student WHERE class between 4 and 6;
 IN- operator allows us to easily test if the expression in the list of values.
mysql> SELECT * FROM Student WHERE class in (4,5,6);
SQL

 Pattern Matching – LIKE Operator
A string pattern can be used in SQL using the following wild card
 % Represents a substring in any length
 _ Represents a single character
Example:
‘A%’ represents any string starting with ‘A’ character.
‘_ _A’ represents any 3 character string ending with ‘A’.
‘_B%’ represents any string having second character ‘B’
‘_ _ _’ represents any 3 letter string.
A pattern is case sensitive and can be used with LIKE operator.
mysql> SELECT * FROM Student WHERE Name LIKE ‘A%’;
mysql> SELECT * FROM Student WHERE Name LIKE ’%Singh%’;
mysql> SELECT Name, City FROM Student WHERE Class>=8 AND Name LIKE
‘%Kumar%’ ;
SQL

mysql> SELECT * FROM Student ORDER BY class;
To get descending order use DESC key word.
mysql> SELECT * FROM Student ORDER BY class DESC;
To display data after removal of duplicate values from specific column.
mysql> select distinct class from student;
Deleting selected rows from a table using the DELETE command
mysql> DELETE FROM student WHERE firstname=“amar";
To modify or update entries in the table use the UPDATE command
mysql> UPDATE student SET class=“V" WHERE firstname=“freya";
SQL

Creating Table with Constraints
The following constraints are commonly used in SQL:
NOT NULL -It Ensures that a column cannot have a NULL value
UNIQUE - It Ensures that all values in a column are different
PRIMARY KEY - A combination of a NOT NULL and UNIQUE. Uniquely
identifies each row in a table
FOREIGN KEY - It Uniquely identifies a row/record in another table
CHECK - It Ensures that all values in a column satisfies a specific
condition
DEFAULT - It Sets a default value for a column when no value is specified
INDEX - It is Used to create and retrieve data from the database very
quickly
SQL

Creating Table with Constraints
mysql> CREATE TABLE Persons (
ID int NOT NULL PRIMARY KEY,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Age int,
City varchar(255) DEFAULT ‘Jaipur',
CONSTRAINT CHK_Person CHECK (Age>=18)
);
mysql> CREATE TABLE Orders (
OrderID int NOT NULL,
OrderNumber int NOT NULL,
PersonID int,
PRIMARY KEY (OrderID),
FOREIGN KEY (PersonID) REFERENCES Persons(ID) );
SQL

Altering Table
The SQL ALTER TABLE command is used to add, delete or modify
columns in an existing table. You should also use the ALTER TABLE
command to add and drop various constraints on an existing table.
Syntax
The basic syntax of an ALTER TABLE command to add a New Column in
an existing table is as follows.
ALTER TABLE table_name ADD column_name datatype;
The basic syntax of an ALTER TABLE command to DROP COLUMN in an
existing table is as follows.
ALTER TABLE table_name DROP COLUMN column_name;
The basic syntax of an ALTER TABLE command to change the DATA TYPE
of a column in a table is as follows.
ALTER TABLE table_name MODIFY COLUMN column_name datatype;
SQL

Altering Table
The basic syntax of an ALTER TABLE command to add a NOT NULL constraint to a column in a table
is as follows.
ALTER TABLE table_name MODIFY column_name datatype NOT NULL;
The basic syntax of ALTER TABLE to ADD UNIQUE CONSTRAINT to a table is as follows.
ALTER TABLE table_name
ADD CONSTRAINT MyUniqueConstraint UNIQUE(column1, column2...);
The basic syntax of an ALTER TABLE command to ADD CHECK CONSTRAINT to a table is as follows.
ADD CONSTRAINT MyUniqueConstraint CHECK (CONDITION);
The basic syntax of an ALTER TABLE command to ADD PRIMARY KEY constraint to a table is as
follows.
ADD CONSTRAINT MyPrimaryKey PRIMARY KEY (column1, column2...);
The basic syntax of an ALTER TABLE command to DROP CONSTRAINT from a table is as follows.
DROP CONSTRAINT MyUniqueConstraint;
SQL

Altering Table
DROP INDEX MyUniqueConstraint;
The basic syntax of an ALTER TABLE command to DROP PRIMARY KEY constraint from a table is as
follows.
DROP CONSTRAINT MyPrimaryKey;
If we are using MySQL, the code is as follows −
DROP PRIMARY KEY;
SQL

MySQL Order By clause is used to sort the table data in
either Ascending order or Descending order. By default,
data is not inserted into Tables in any order unless we have
an index.
So, If we want to retrieve the data in any particular order,
we have to sort it by using MySQL Order By statement.
Syntax:-SELECT Column_Names
FROM Table_Name
ORDER BY {Column1}[ASC | DESC] {Column2}[ASC | DESC]
SQL

MySQL Order by– e.g.
Suppose we are having student table with following data.
Now we write the query – select * from student order by class;
Query result will be in ascending order of class.If we not specify asc/desc in
query then ascending clause is applied by default
SQL

Now we write the query – select * from student order by class desc;
Query result will be in descending order of class
SQL

MySQL Order by – e.g.
Now we write query–select * from student order by class asc, marks asc;
Query result will be ascending order of class and if same class exists
then ordering will done on marks column(ascending order)
SQL

Now we write query–select * from student order by class asc, marks desc;
Query result will be ascending order of class and if same class exists
then ordering will done on marks column(descending order)
SQL

An aggregate function performs a calculation on multiple values
and returns a single value. For example, you can use the AVG()
aggregate function that takes multiple numbers and returns the
average value of the numbers.Following is the list of aggregate
functions supported by mysql.
Name Purpose
SUM() Returns the sum of given column.
MIN() Returns the minimum value in the given column.
MAX() Returns the maximum value in the given column.
AVG() Returns the Average value of the given column.
COUNT() Returns the total number of values/ records as per given
column.
SQL

Aggregate Functions & NULL
Consider a table Emp having following records as-
Null values are excluded while (avg)aggregate function is used
SQL Queries
mysql> Select Sum(Sal) from EMP;
mysql> Select Min(Sal) from EMP;
mysql> Select Max(Sal) from EMP;
mysql> Select Count(Sal) from EMP;
mysql> Select Avg(Sal) from EMP;
mysql> Select Count(*) from EMP;
Emp
Code Name Sal
E1 Mohak NULL
E2 Anuj 4500
E3 Vijay NULL
E4 Vishal 3500
E5 Anil 4000
Result of query
12000
3500
4500
3
4000
5
SQL

The GROUP BY clause groups a set of rows/records into a
set of summary rows/records by values of columns or
expressions. It returns one row for each group.
We often use the GROUP BY clause with aggregate
functions such as SUM, AVG, MAX, MIN, and COUNT. The
aggregate function that appears in the SELECT clause
provides information about each group.
The GROUP BY clause is an optional clause of the SELECT
statement.
Syntax –
SELECT 1, c2,..., cn, aggregate_function(ci)
FROM table WHERE where_conditions GROUP BY c1 , c2,...,cn;
Here c1,c2,ci,cn are column name
SQL

MySQL group by – e.g.
Now we write query–select class from student group by class;
Query result will be unique occurrences of class values,just similar
to use distinct clause like(select distinct class from student).
SQL

MySQL GROUP BY with aggregate functions
The aggregate functions allow us to perform the calculation of a set of rows and return a
single value. The GROUP BY clause is often used with an aggregate function to perform
calculation and return a single value for each subgroup.
For example, if we want to know the number of student in each class, you can use the
COUNT function with the GROUP BY clause as follows:Suppose we are having student table
with following data.
Now we write query–select class,count(*) from student group by class;
Query result will be unique occurrences of class values along with counting of
students(records) of each class(sub group).
SQL

MySQL GROUP BY with aggregate functions
we are having student table with following data.
Now we write query–select class,avg(marks) from student group by class;
Query result will be unique occurrences of class values along with average
marks of each class(sub group).
SQL

MySQL GROUP BY with aggregate functions (with where and order by clause)
Now we write query–select class,avg(marks) from student where class<10 group
by class order by marks desc;
Query result will be unique occurrences of class values where class<10 along with
average marks of each class(sub group) and descending ofer of marks.
SQL

The HAVING clause is used in the SELECT
statement to specify filter conditions for a
group of rows or aggregates. The HAVING
clause is often used with the GROUP BY
clause to filter groups based on a specified
condition. To filter the groups returned by
GROUP BY clause, we use a HAVING clause.
WHERE is applied before GROUP BY, HAVING
is applied after (and can filter on aggregates).
SQL

MySQL GROUP BY with aggregate functions & having clause
Now we write query–select class,avg(marks) from student group by class
having avg(marks)<90;
marks of each class(sub group) and each class having average marks<90.
SQL

MySQL GROUP BY with aggregate functions & having clause
Now we write query–select class,avg(marks) from student group by class
having count(*)<3;
marks of each class(sub group) and each class having less than 3 rows.
SQL

Cartesian product (X)/cross joint
Cartesian Product is denoted by X symbol.
Lets say we have two relations R1 and R2
then the cartesian product of these two
relations (R1 X R2) would combine each tuple
of first relation R1 with the each tuple of
second relation R2.
SQL

Cartesian product (X) example
Table a and Table b as shown
below
Mysql query –
Select * from a,b;
Select * from a cross join b;
Degree of cartesion product is 3 and cardinality is 4=(2 rows of a X 2 rows of b)
SQL

Join – Join is used to fetch data from two or more tables,
which is joined to appear as single set of data. It is used for
combining column from two or more tables by using values
common to both tables.
Types of JOIN
Following are the types of JOIN that we can use in SQL:
• Inner
• Outer
• Left
• Right
SQL

INNER Join or EQUI Join⋈
This is a simple JOIN in which the result is
based on matched data as per the equality
condition specified in the SQL query.
SQL

INNER Join or EQUI Join example
Table a and Table b as shown below
Mysql query –
Select course.student_name from
couse , student where
course.student_name=student.stude
nt_name;
Select a.name from a inner join b
where a.name=b.name;
SQL

Natural JOIN(⋈)
Natural Join is a type of Inner join which is based on
column having same name and same datatype present
in both the tables to be joined.E.g.
Select * from a natural join b;
SQL

LEFT Outer Join
The left outer join returns a resultset table with the matched data from the
two tables and then the remaining rows of the left table and null from the
right table's columns. E.g.
Mysql query –
Select * from a left outer join b on
(a.name=b.name);
SQL

RIGHT Outer Join
The right outer join returns a resultset table with the matched data from the
two tables being joined, then the remaining rows of the right table and null
for the remaining left table's columns.E.g.
Mysql query –
Select * from a right outer join b on
(a.name=b.name);
SQL

Full Outer Join
The full outer join returns a resultset table with the matched data of two
table then remaining rows of both left table and then the right table.E.g.
Mysql query –
Select * from a left outer join b on
(a.name=b.name) union Select * from
a right outer join b on
(a.name=b.name) ;
SQL

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