How many Types of Relationship Exist in Database Designing?

There are three major relationship models:

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  One-to-one
  
  

  
  
  
  

   One-to-One relationship ER diagram
  
  



• One-to-many
  In this many records in one table correspond to the one record in another table.
  Example: Every one customer can have multiple sales. So there exist one-to-many relationships between customer and sales table.
  

  One Asset can have multiple Maintenance. So Asset entity has one-to-many relationship between them as the ER model shows below.

  
  

  

  
  
  
  

  One-to-Many Relationship ER diagram
  
  



• Many-to-many
  In this, one record in one table corresponds to many rows in another table and also vice-versa.
  For instance: In a company, one employee can have many skills like Java , C# etc. and also one skill can belong to many employees.
  

  Given below is a sample of many-to-many relationship. One employee can have knowledge of multiple Technology. So in order to implement this, we have one more table Employee Technology which is linked to the primary key of Employee and Technology table.

  
  

  

  
  
  
  

   Many-to-Many Relationship ER diagram