1Z0-006 Relational Data Model 5 — Questions and Answers
Question 1: First Normal Form (1NF) requires that all column values in a table must be:
- Unique across the entire table
- Atomic (indivisible, single-valued) (Correct answer)
- Non-null
- Derived from the primary key
Correct answer: Atomic (indivisible, single-valued)
1NF requires each cell to hold a single, atomic value; no repeating groups or multi-valued attributes are allowed.
Question 2: A self-referencing (recursive) foreign key means a table's foreign key references:
- Another table's primary key
- Its own primary key in the same table (Correct answer)
- A unique key in a view
- A sequence value
Correct 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.
Question 3: Which SQL command removes all rows from a table quickly without logging individual row deletions and cannot be rolled back by default in Oracle?
- DELETE
- DROP
- TRUNCATE (Correct answer)
- REMOVE
Correct 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.
Question 4: Which type of integrity ensures that a foreign key value either matches an existing primary key value or is NULL?
- Entity integrity
- Referential integrity (Correct answer)
- Domain integrity
- User-defined integrity
Correct answer: Referential integrity
Referential integrity guarantees that every foreign key value references a valid primary key in the parent table or is NULL.
Question 5: In the Entity-Relationship model, which symbol on a crow's foot diagram represents 'one and only one'?
- Crow's foot (three lines)
- Single vertical line (Correct answer)
- Circle
- Double vertical line
Correct answer: Single vertical line
A single vertical line (or perpendicular stroke) in crow's foot notation represents a cardinality of exactly one.
Question 6: Which Oracle constraint type can reference columns in the same row to enforce a business rule, such as END_DATE >= START_DATE?
- FOREIGN KEY
- PRIMARY KEY
- CHECK (Correct answer)
- NOT NULL
Correct answer: CHECK
A CHECK constraint can compare columns within the same row and enforce business rules like END_DATE >= START_DATE.
Question 7: Which relational operation extracts a subset of columns from a table, producing a new relation with fewer attributes?
- Selection (restrict)
- Projection (Correct answer)
- Join
- Union
Correct answer: Projection
Projection in relational algebra picks specific columns from a relation, equivalent to listing only certain columns in a SELECT statement.
1Z0-006 Relational Data Model 5
First Normal Form (1NF) requires that all column values in a table must be: