RDBMS

Data in an RDBMS is stored in tables (relations). A table has:

• A header row containing attribute (column) names
• Subsequent rows containing data records (tuples)

A record (also called a row or tuple) holds all the column values for one entity instance. Example: a student's row containing roll number, name, age, GPA, year.

A column (attribute) contains values of a particular property for all rows in a table (stored vertically). Example: the name column contains the names of all students.

Field usually refers to a single cell value in a table (intersection of a row and a column). Collectively, fields (columns) define the schema or structure of the table (e.g., Roll_No, Name, Age, GPA, Year).

Constraints are checks enforced by the DBMS to ensure data integrity and validity. If a constraint is violated, the DBMS rejects the operation.

Common SQL constraints:

• DEFAULT — supplies a default value when none is provided
• NOT NULL — disallows NULL values
• UNIQUE — enforces uniqueness across rows
• CHECK — enforces a boolean condition on column values
• PRIMARY KEY — uniquely identifies each row
• FOREIGN KEY — enforces referential integrity between tables
• DOMAIN constraints — restrict allowed values (type/range)