Database Management Systems and Data Handling
What this domain tests
Database Management Systems and Data Handling tests how data is stored, related, queried and protected: tables, keys, data types, SQL statements, validation and backup.
Core rules and concepts
- A database is an organised collection of related data; a DBMS is software that creates, manages and queries it. In a relational database, data sits in tables (relations).
- A row is a record or tuple; a column is a field or attribute. Each field has a data type such as text, number, date or yes/no.
- A primary key uniquely identifies each record and cannot be NULL. A foreign key is a field in one table that refers to the primary key of another table, creating a relationship.
- SQL: SELECT retrieves, INSERT adds, UPDATE changes and DELETE removes rows. WHERE filters rows; ORDER BY sorts; DISTINCT removes duplicates.
- Validation (data type, range, required, format) stops bad input. Backup and access control protect data.
Worked example
Table Student(Name, Marks). Query: SELECT Name FROM Student WHERE Marks >= 60 ORDER BY Name; Reasoning: SELECT chooses the Name column; FROM names the table; WHERE keeps only rows with Marks at least 60; ORDER BY Name sorts the result alphabetically. It does not change the stored table.
Traps that cost marks
Primary key and foreign key are commonly swapped. DELETE removes rows; DROP removes the table. NULL means unknown, not zero. SELECT * returns all columns. A query result is not a new saved table unless you create one.