Database Concepts and Data Management
This domain tests the relational model: how data is stored in tables, why keys matter, and how to write simple SQL. Expect definitions, key identification, data types, normalization basics, and query reading.
Core rules and concepts
- A DBMS stores, retrieves, and controls access to data. A relational database stores data in tables (relations).
- A row is a record or tuple; a column is a field or attribute. A primary key uniquely identifies each row and cannot be NULL. A candidate key is any minimal unique key; one becomes primary. A foreign key references a primary key in another table and enforces referential integrity.
- Common data types: INTEGER, VARCHAR, DATE, BOOLEAN. Choose the type that matches the values and operations.
- SQL basics: SELECT columns FROM table WHERE row condition ORDER BY column. Use single quotes for text literals.
- Normalization reduces redundancy: 1NF removes repeating groups and requires atomic values; 2NF removes partial dependencies; 3NF removes transitive dependencies.
- Forms and reports are user interfaces; tables store the base data.
Worked example
Table Student(RollNo, Name, Marks, City) with RollNo as primary key. Query: SELECT Name FROM Student WHERE Marks >= 60 ORDER BY Name; Reasoning: SELECT chooses the Name column, FROM names the table, WHERE filters rows to marks of 60 or more, and ORDER BY sorts names ascending. The query returns only names, not whole records. If two students have the same marks, both still appear because no DISTINCT is used.
Traps that cost marks
A primary key is not a foreign key. NULL means unknown, not zero or blank. DELETE removes rows; DROP removes the table structure. WHERE filters rows before grouping; HAVING filters groups. Duplicate values are allowed in non-key columns.