Database.What are the types of relationships in a database? Give examples.

In relational databases, relationships define how data in one table is connected to data in another. There are three main types of relationships:

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1. 🔁 One-to-One (1:1)

➡️ One record in Table A is related to only one record in Table B, and vice versa.

✅ Example:

Table: Users

UserID	Name
1	Alice

Table: UserProfiles

ProfileID	UserID	Bio
101	1	Developer

• Each user has only one profile
• UserID in UserProfiles is a foreign key referencing Users(UserID)

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2. 🔗 One-to-Many (1:N)

➡️ One record in Table A can be related to many records in Table B,
but each record in Table B is related to only one in Table A.

✅ Example:

Table: Customers

CustomerID	Name
1	Alice
2	Bob

Table: Orders

OrderID	CustomerID	Product
101	1	Laptop
102	1	Phone
103	2	Monitor

• One customer can place many orders
• Each order belongs to one customer

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3. 🔄 Many-to-Many (M:N)

➡️ A record in Table A can relate to many records in Table B, and vice versa.

To implement this, we use a junction table.

✅ Example:

Table: Students

StudentID	Name
1	Alice
2	Bob

Table: Courses

CourseID	Title
101	Math
102	Physics

Junction Table: StudentCourses

StudentID	CourseID
1	101
1	102
2	101

• Alice takes Math and Physics
• Bob takes Math
• This is a many-to-many relationship

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🧠 Summary Table:

Relationship	Description	Example
One-to-One	One row in A ↔ one row in B	User ↔ Profile
One-to-Many	One row in A ↔ many in B	Customer ↔ Orders
Many-to-Many	Many rows in A ↔ many in B via junction	Students ↔ Courses