Database Concepts and Data Management
This domain tests database vocabulary, why databases beat paper registers, and simple query writing.
Core rules
- Data are raw facts; information is processed data. A DBMS is software to create, store, retrieve and secure a database; an RDBMS stores data in related tables.
- Table = relation; row = record or tuple; column = field or attribute; domain = the allowed values for a field.
- Primary key: uniquely identifies each row and cannot be NULL. Foreign key: a field in one table that refers to the primary key of another table, enforcing referential integrity.
- Common data types: Text/Short Text, Number, Date/Time, Currency, Yes/No. Choosing the wrong type, such as storing a phone number as Number, loses leading zeros.
- Objects: table stores, query asks, form enters, report prints.
- SQL pattern: SELECT columns FROM table WHERE condition ORDER BY column;
Worked example
Student(RollNo, Name, Class, City) with 40 rows. RollNo is the primary key: unique and never blank. Name is not - two students can be called Anil. City is not - many students share Jaipur. Query: SELECT Name, Class FROM Student WHERE City = 'Jaipur' ORDER BY Name; Reasoning: SELECT chooses columns, WHERE filters rows, ORDER BY sorts. The output is a result set, not a new stored table unless you save it.
Traps
- Swapping field and record.
- Saying a primary key may be NULL or duplicated.
- Confusing a query (retrieves) with a form (enters).
- Forgetting quotes around text values in WHERE.
- Assuming one big table is enough; redundancy causes update anomalies.