Tables, Keys, and Constraints in DBMS
Tables, Keys, and Constraints in DBMS
The relational model in DBMS is based on organizing data into tables. Each table consists of rows and columns, and relationships between tables are maintained using keys and constraints. Understanding tables, keys, and constraints is essential for designing efficient and reliable databases.
In this lesson, you will learn the core components of the relational model and how they are used in real-world database systems.
What is a Table in DBMS?
A table (also called a relation) is a structured format used to store data in rows and columns.
- Rows represent records (tuples)
- Columns represent attributes (fields)
Example: Student Table
- Student_ID
- Name
Tables are the foundation of relational databases like MySQL.
What are Keys in DBMS?
Keys are used to uniquely identify records and establish relationships between tables.
Types of Keys
1. Primary Key
A primary key uniquely identifies each record in a table.
- Cannot have duplicate values
- Cannot be NULL
Example: Student_ID
2. Foreign Key
A foreign key is used to link two tables together.
- References the primary key of another table
- Maintains relationships
3. Candidate Key
A candidate key is a set of attributes that can uniquely identify a record.
4. Composite Key
A composite key consists of two or more attributes used together to uniquely identify a record.
What are Constraints in DBMS?
Constraints are rules applied to columns in a table to ensure data integrity and accuracy.
Types of Constraints
1. NOT NULL
Ensures that a column cannot have NULL values
2. UNIQUE
Ensures all values in a column are different
3. PRIMARY KEY
Ensures unique identification of records
4. FOREIGN KEY
Maintains referential integrity between tables
5. CHECK
Ensures that values meet a specific condition
Real-World Example
Table: Students
- Student_ID (Primary Key)
- Name
- Course_ID (Foreign Key)
Table: Courses
- Course_ID (Primary Key)
- Course_Name
This structure creates a relationship between students and courses using keys.
Why Tables, Keys, and Constraints are Important
They help you:
- Organize data efficiently
- Maintain data integrity
- Avoid duplicate data
- Build scalable database systems
FAQs
What is a table in DBMS?
A table is a structured format of rows and columns used to store data.
What is a primary key?
A primary key uniquely identifies each record in a table.
What is a foreign key?
A foreign key links two tables and maintains relationships.
Why are constraints important?
Constraints ensure data accuracy, consistency, and integrity.
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