Relational Data Model Flashcards

First Normal Form (1NF) requires that all column values in a table must be:

Answer: Atomic (indivisible, single-valued)

1NF requires each cell to hold a single, atomic value; no repeating groups or multi-valued attributes are allowed.

A self-referencing (recursive) foreign key means a table's foreign key references:

Answer: Its own primary key in the same table

A self-referencing foreign key points back to the primary key of the same table, commonly used to model hierarchies like an employee-manager relationship.

Which SQL command removes all rows from a table quickly without logging individual row deletions and cannot be rolled back by default in Oracle?

Answer: TRUNCATE

TRUNCATE removes all rows using a DDL operation that deallocates data pages; it cannot be rolled back because it does not generate per-row undo logs.

Which type of integrity ensures that a foreign key value either matches an existing primary key value or is NULL?

Answer: Referential integrity

Referential integrity guarantees that every foreign key value references a valid primary key in the parent table or is NULL.

In the Entity-Relationship model, which symbol on a crow's foot diagram represents 'one and only one'?

Answer: Single vertical line

A single vertical line (or perpendicular stroke) in crow's foot notation represents a cardinality of exactly one.

Which Oracle constraint type can reference columns in the same row to enforce a business rule, such as END_DATE >= START_DATE?

Answer: CHECK

A CHECK constraint can compare columns within the same row and enforce business rules like END_DATE >= START_DATE.

Which relational operation extracts a subset of columns from a table, producing a new relation with fewer attributes?

Answer: Projection

Projection in relational algebra picks specific columns from a relation, equivalent to listing only certain columns in a SELECT statement.