What types of relationships exist between entities in a database?

In databases, the following main types of relationships exist between entities:

1. One-to-One

   • Each record in one table is related to one record in another.
   • Example: each user has one profile.

2. One-to-Many

   • One record in the first table is related to multiple records in the second.
   • Example: one author can have many books.

3. Many-to-Many

   • Records in one table are related to multiple records in another and vice versa.
   • Implemented through an intermediate table.
   • Example: students and courses — a student can attend many courses, and a course can have many students.

These relationships define how data is connected and how queries are constructed to retrieve related data.