1Z0-006 Relational Data Model 4 — Questions and Answers
Question 1: Which type of key is a system-generated unique identifier (such as a sequence value) with no business meaning?
- Natural key
- Candidate key
- Surrogate key (Correct answer)
- Composite key
Correct answer: Surrogate key
A surrogate key is an artificially generated identifier (e.g., from an Oracle SEQUENCE) that has no inherent business meaning.
Question 2: What does cardinality describe in the context of a database table?
- The number of columns in the table
- The number of rows in the table (Correct answer)
- The number of indexes on the table
- The number of constraints on the table
Correct answer: The number of rows in the table
Cardinality refers to the number of rows (tuples) currently in a relation (table).
Question 3: Which SQL clause is used to filter groups after a GROUP BY has been applied?
- WHERE
- HAVING (Correct answer)
- FILTER
- AND
Correct answer: HAVING
The HAVING clause filters grouped results after aggregation, while WHERE filters individual rows before grouping.
Question 4: In a relational table, what is a tuple?
- A column definition
- A single row of data (Correct answer)
- A table constraint
- A key-value pair index
Correct answer: A single row of data
In relational theory, a tuple corresponds to a single row in a table, representing one complete record.
Question 5: Which type of JOIN returns all rows from the left table and matching rows from the right table, with NULLs for unmatched right rows?
- INNER JOIN
- RIGHT OUTER JOIN
- LEFT OUTER JOIN (Correct answer)
- FULL OUTER JOIN
Correct answer: LEFT OUTER JOIN
A LEFT OUTER JOIN includes all rows from the left table; where no match exists in the right table, NULL values are returned for right-table columns.
Question 6: Which Oracle object provides a reusable, auto-incrementing number generator often used to populate surrogate primary keys?
- INDEX
- SYNONYM
- SEQUENCE (Correct answer)
- TRIGGER
Correct answer: SEQUENCE
An Oracle SEQUENCE is a database object that generates unique numeric values in order, commonly used with NEXTVAL to populate primary key columns.
Question 7: Which property of a relational table means that rows have no inherent ordering?
- Atomicity
- Set-based storage (Correct answer)
- Domain constraint
- Referential integrity
Correct answer: Set-based storage
In the relational model, tables are sets of tuples with no defined order; any ordering must be explicitly requested via ORDER BY.
1Z0-006 Relational Data Model 4
Which type of key is a system-generated unique identifier (such as a sequence value) with no business meaning?