Joins

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 Joins:
 Cartesian Product
 Natural Join
 Equi Join
 Self Join
 Inner Join
 outer Join(Left, Right, Full)

JOINS
 A JOIN combines together information from two or
more tables into one result set.
 The records from the table are fetched based on
some values that are common to each.
 It can also specifies some condition while
retrieving the data.
 Join = cross product + some condition

Cartesian product
 Before understanding JOINS in SQL we
should know about Cartesian Product.
 Also known as Cross Product.

Cartesian Product in sets(Mathematics)
 A = { 1, 2, 3} B = { a , b}
 A x B = { (1,a) , (2,a), (3,a), (1, b), (2,b) , (3,b) }

Cartesian product
 R1 R2
 R1 x R2
A B
2 E1
4 E2
5 E3
B C
E1 5
E5 7
A B B C
2 E1 E1 5
4 E2 E1 5
5 E3 E1 5
.. .. .. ..

Cartesian product
 R1 R2
 R1 x R2
A B
2 E1
4 E2
5 E3
B C
E1 5
E5 7
A B B C
2 E1 E1 5
4 E2 E1 5
5 E3 E1 5
2 E1 E5 7
4 E2 E5 7
5 E3 E5 7

Cartesian product of two table
QUERY: select * from emp2,dept;

Cartesian Product :
 Cartesian Product is the all possible combinations
between applied table rows.
 Suppose two tables are T1 and T2
 T1 has r1 rows and c1 columns
 T2 has r2 rows and c2 columns
 Cartesian product of T1 and T2 will have:
 r1 * r2 rows and c1 + c2 columns.

Natural Join: Common columns in both the tables
must have same name.
After Natural Join :
 Select * from R1, R2
where R1.B=R2.B;
OR Select *
from R1 natural join R2;
=
A B
2 E1
4 E2
5 E3
B C
E1 5
E2 7
A B B C
2 E1 E1 5
4 E2 E1 5
5 E3 E1 5
2 E1 E2 7
4 E2 E2 7
5 E3 E2 7
A B C
2 E1 5
4 E2 7

Natural JOIN:
Select * from Emp2 natural join Dept;
- Behaves Same as Inner Join
- In Natural Join common attribute must have
same name in both the tables

Example:
 Select emp_name, loc from Emp2 natural join Dept
where loc= 'NEW YORK';

Equi Join
 R1 R2
 After Equi Join :
 Select *from R1,R2
 where R1.B=R2.C;
 or Select *from R1 join R2
 on R1.B=R2.C;
A B
2 E1
4 E2
5 E3
C D
E1 5
E2 7
A B C D
2 E1 E1 5
4 E2 E1 5
5 E3 E1 5
2 E1 E2 7
4 E2 E2 7
5 E3 E2 7
A B C D
2 E1 E1 5
4 E2 E2 7

Equi Join:
 Same as inner join , it uses only equality
comparison.
 Query : Select * from Emp2, dept where
emp2.deptno=dept.deptno;

Self Join
 A self Join is a type of Join which is used to join a
table to itself. In this join both the columns belongs
to the same table.
 Syntax :
 Select T1.column, T1.column from T1 A inner join T2 B on
A.column= B.column

Self Join
 R1
After Equi Join :
Select T.B
from R1 T, R1 S
where T.A=S.A
and T.B <> S.B;
A B
2 E1
2 E2
5 E3
A B A B
2 E1 2 E1
2 E2 2 E1
5 E3 2 E1
2 E1 2 E2
2 E2 2 E2
5 E3 2 E2
2 E1 5 E3
2 E2 5 E3
5 E3 5 E3
B
E2
E1

Select * from Emp2 A , Emp2 B
where A.Deptno = B.Deptno;

Inner Join
 Inner Join combines the rows retrieved from
multiple tables on the basis of common columns of
the tables.
 It takes that rows from the cartesian product table
where the join elements ( emp.deptno and
dept.deptno in the above query) matches fully
 Syntax:
 Select T1.column, T2.column from T1 inner join T2
on T1.column=T2.column

Inner Join
 R1 R2
 After Inner Join
=
A B
2 E1
4 E2
5 E3
B C
E1 5
E2 7
A B B C
2 E1 E1 5
4 E2 E1 5
5 E3 E1 5
2 E1 E2 7
4 E2 E2 7
5 E3 E2 7
A B B C
2 E1 E1 5
4 E2 E2 7

Select * from Emp2 inner join Dept on
Emp2.Deptno = Dept.Deptno

example
 Select * from Emp2 inner join Dept on
Emp2.Deptno = Dept.Deptno
where loc= 'NEW YORK';

Example:
 Select emp_name,loc from Emp2 inner join Dept
on Emp2.Deptno = Dept.Deptno where loc= 'NEW
YORK';

Left Outer Join
 Left outer Join takes that rows which are in inner
join output.
 And it also looks for the rows in the left table
which are not in the inner join output.
 The rows are added to the output with null in right
columns.

Left Join
 R1 R2
 After Left Join
=
A B
2 E1
4 E2
5 E3
B C
E1 5
E2 7
A B B C
2 E1 E1 5
4 E2 E1 5
5 E3 E1 5
2 E1 E2 7
4 E2 E2 7
5 E3 E2 7
A B B C
2 E1 E1 5
4 E2 E2 7
5 E3 NUL
L
NUL
L

Syntax:
 Select T1.column, T2.column from T1 left outer
join T2 on T1.column=T2.column
Eg. Select * from Emp2 left outer join Dept on
Emp2.Deptno = Dept.Deptno;

Right Outer Join
 Right outer Join takes that rows which are in inner
join output.
 And it also looks for the rows in the right table
which are not in the inner join output.
 The rows are added to the output with null in left
columns.

Right Join
 R1 R2
 After right Join
=
A B
2 E1
4 E2
5 E3
B C
E1 5
E5 7
A B B C
2 E1 E1 5
4 E2 E1 5
5 E3 E1 5
2 E1 E5 7
4 E2 E5 7
5 E3 E5 7
A B B C
2 E1 E1 5
NULL NULL E5 7

Syntax:
 Select T1.column, T2.column from T1 right outer
Eg. Select * from Emp2 right outer join Dept on

Full Outer Join
 Full outer Join takes that rows which are in inner
join output.
 And it also looks for the rows in the left and also
right table which are not in the inner join output.

Full Join
 R1 R2
 After Full Join
=
A B
2 E1
4 E2
5 E3
B C
E1 5
E5 7
A B B C
2 E1 E1 5
4 E2 E1 5
5 E3 E1 5
2 E1 E5 7
4 E2 E5 7
5 E3 E5 7
A B B C
2 E1 E1 5
NULL NULL E5 7
4 E2 NULL NULL
5 E3 NULL NULL

Syntax:
 Select T1.column, T2.column from T1 full outer
Eg. Select * from Emp2 full outer join Dept on

Consider two table
Student Faculty
S_id S_name course
1 Amit BCA
2 Ram Btech
3 Hardik BCA
4 Pawan BCA
5 Sumit Btech
6 Aman MCA
7 Hardik BCA
F_Id course Loc
F1 BCA AB 10
F2 Btech AB 1
F3 MTech AB1

 Cartesian product:
 Select * from Student, Faculty;
 Natural Join:
 Select * from Student natural join Faculty
 Equi join:
 Select * from student join Faculty on
Student.course=Faculty.course
 Self join:
 Select A.S_name from Student A, Student B where
A.S_id= B.S_id

 Inner Join:
 Select Student.S_name from Student inner join
Faculty on Student.course= Faculty.course where
Faculty.loc=‘AB10’
 Left Join:
 Select Student.S_name from Student left outer join
 Right Join:
 Select Student.S_name from Student right outer join

Joins

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