SQL

Reena P V

PGT CS

KV Payyanur

- JOINS

Objectives:

To understand the requirement of

SQL Joins

Identify and demonstrate the proper

use of inner join , outer join clauses.

INTRODUCTION - SQL JOINS

SQL Joins are essential to display

data from more than one table.

SQL JOIN clause is used to

combine rows from two or more

tables, based on a common field

between them..

TYPES

Cross Join

Equi Join

Non Equi Join

Inner Join

Outer Join

C artesian Product (Cross Join)

Cartesian product of two tables is

obtained by pairing up each row of

one table with each row of the other

table.

C artesian Product (Cross Join)

SELECT * FROM order_table, product_table;

C artesian Product (Cross Join)

SELECT * FROM order_table, product_table;

Order_No P_code Sup_Code Code Name

1 P001 S002 P001 Toothpaste

2 P002 S002 P001 Toothpaste

1 P001 S002 P002 Shampoo

2 P002 S002 P002 Shampoo

1 P001 S002 P003 Conditioner

2 P002 S002 P003 Conditioner

Each row of the first table (Order_table) is paired with each

row of the second table (Product).

C artesian Product (Cross Join)

The number of columns in the Cartesian

product is the sum of the number of columns

in both the tables

The number of rows in the Cartesian

product is the product of rows of the tables

C artesian Product (Cross Join)

E qui-Join of Tables

• A join which is obtained by putting a

condition of equality on cross join is

called an 'equi join'.

• It is a simple join condition that uses ‘= ‘

sign

as a comparison operation .

• we can extract meaningful information

from

the Cartesian product by placing some

Eg:

SELECT * FROM order, product

WHERE order.O_code = product.P_code;

E qui-Join of Tables

Qualifying the column name

SELECT Order_No, Order_table.Sup_Code, Name,

Address FROM order_table, supplier

WHERE order_table.sup_code = supplier.sup_code;

Extracting values by putting condition (filtering)

SELECT * FROM order, product

WHERE order.O_code = product.P_code and qty>100;

Non Equi Join

A JOIN that uses comparison

operator instead of the equal sign

like >, <, >=, <= along with

conditions.

Inner Join

An inner join is a type of join

where we use = and <> in the

where condition joining the

tables.

ROLLNO NAME

1 ROHAN

2 JAYA

3 TEENA

4 DIKSHA

5 SUMA

Table : A

ROLL NO FEES

3 4500

4 3500

5 5000

6 6000

Table : B

SELECT A. ROLLNO, NAME ,FEES FROM A,B

WHERE A. ROLLNO= B.ROLLNO;

ROLLNO NAME FEES

3 TEENA 4500

4 DIKSHA 3500

5 SUMA 5000

SELECT A. ROLLNO, NAME ,FEES FROM A INNER JOIN B

ON A. ROLLNO= B.ROLLNO;

OUTER JOIN

LEFT OUTER JOIN

RIGHT OUTER JOIN

FULL OUTER JOIN

A left outer join, or left join, results in

a set where all of the rows from the

first table are preserved.

The rows from the second, or right

hand side table only show up if they

have a match with the rows from the

first table.

Where there are values from the left

table but not from the right, the table

will read null.

ROLLNO NAME

1 ROHAN

2 JAYA

3 TEENA

4 DIKSHA

5 SUMA

Table : A

ROLL NO FEES

3 4500

4 3500

5 5000

6 6000

Table : B

SELECT A. ROLLNO, NAME ,FEES FROM A

LEFT OUTER JOIN B ON A. ROLLNO= B.ROLLNO;

ROLLNO NAME FEES

1 ROHAN NULL

2 JAYA NULL

3 TEENA 4500

4 DIKSHA 3500

5 SUMA 5000

RIGHT OUTER JOIN……….?

ROLLNO NAME

1 ROHAN

2 JAYA

3 TEENA

4 DIKSHA

5 SUMA

Table : A

ROLL NO FEES

3 4500

4 3500

5 5000

6 6000

Table : B

SELECT A. ROLLNO, NAME ,FEES FROM A

RIGHT OUTER JOIN B ON A. ROLLNO=

B.ROLLNO;

ROLLNO NAME FEES

3 TEENA 4500

4 DIKSHA 3500

5 SUMA 5000

NULL NULL 6000

FULL OUTER JOINThe full outer join returns a result table with

the matched data of two table then remaining

rows of both left table and then the right table.

ROLLNO NAME FEES

3 TEENA 4500

4 DIKSHA 3500

5 SUMA 5000

1 ROHAN NULL

2 JAYA NULL

NULL NULL 6000

NATURAL JOIN

The JOIN in which only one of the

identical columns coming from joined

tables exists called natural join.

i.e In the result common column will

appear only once.

LOAN NO BRANCH AMOUNT

L1 B1 1000

L2 B2 2000

L3 B3 1500

Table : LOAN

CUST NO LOAN NO

C1 L1

C2 L2

C3 L4

Table : BORROWER

SELECT * FROM LOAN NATURAL JOIN

BORROWER;

LOAN NO BRANCH AMOUNT CUST_NO

L1 B1 1000 C1

L2 B2 2000 C2

SELF JOIN

A self-join is a query in which a table

is joined (compared) to itself. Self-

joins are used to compare values in a

column with other values in the same

column in the same table

EMP_ID NAME MGR_ID

1 Rakesh 3

2 Sudarsh 1

3 Rohit Null

4 Mukesh 1

5 Sushil 1

Table : Employee

SELECT E. NAME AS EMPLOYEE , M.NAME

AS MANAGER FROM Employee E JOIN

Employee M ON E. MGR_ID= M.EMP_ID

EMPLOYEE MANAGER

Rakesh Rohit

Sudarsh Rakesh

Rohit NULL

Mukesh Rakesh

Sushil Rakesh

What is the difference between

EQUI JOIN and NATURAL JOIN ?

A…........Join is made possible by

aliasing the original table.