Entity Relationship Model

Student

student id	name	join date
101	Rachel Green	2000-05-01
201	Joey Tribianni	1998-07-05
301	Monica Geller	1999-12-14
401	Cosmo Kramer	2001-06-05

Courses

student id	semester	course
101	Semester 1	DBMS
101	Semester 1	Calculus
201	Semester 1	Algebra
201	Semester 1	Web

One to One Mapping

Student

student id	name	join date
101	Rachel Green	2000-05-01
201	Joey Tribianni	1998-07-05
301	Monica Geller	1999-12-14
401	Cosmo Kramer	2001-06-05

Studentdetails

student id	SSN	DOB
101	123-56-7890	1980-05-01
201	236-56-4586	1979-07-05
301	365-45-9875	1980-12-14
401	148-89-4758	1978-06-05

For every row on the left-hand side, there will be only one matching entry on the right-hand side.

For student id 101, you will find one SSN and one DOB.

One to Many Mapping

Student

student id	name	join date
101	Rachel Green	2000-05-01
201	Joey Tribianni	1998-07-05
301	Monica Geller	1999-12-14
401	Cosmo Kramer	2001-06-05

Address

student id	address id	address	address type
101	1	1 main st, NY	Home
101	2	4 john blvd,NJ	Dorm
301	3	3 main st, NY	Home
301	4	5 john blvd,NJ	Dorm
201	5	12 center st, NY	Home
401	6	11 pint st, NY	Home

What do you notice here?

Every row on the left-hand side has one or more rows on the right-hand side.

For student id 101, you will notice the home address and Dorm address.\

Many to Many Mapping

Student

student id	name	join date
101	Rachel Green	2000-05-01
201	Joey Tribianni	1998-07-05
301	Monica Geller	1999-12-14
401	Cosmo Kramer	2001-06-05

Student Courses

student id	course id
101	c1
101	c2
301	c1
301	c3
201	c3
401	c4

Courses

course id	course name
c1	DataBase
c2	Web Programming
c3	Big Data
c4	Data Warehouse

What do you notice here?

Students can take more than one course, and courses can have more than one student.