Relational Data Model Flashcards

Which type of key is a system-generated unique identifier (such as a sequence value) with no business meaning?

Answer: Surrogate key

A surrogate key is an artificially generated identifier (e.g., from an Oracle SEQUENCE) that has no inherent business meaning.

What does cardinality describe in the context of a database table?

Answer: The number of rows in the table

Cardinality refers to the number of rows (tuples) currently in a relation (table).

Which SQL clause is used to filter groups after a GROUP BY has been applied?

Answer: HAVING

The HAVING clause filters grouped results after aggregation, while WHERE filters individual rows before grouping.

In a relational table, what is a tuple?

Answer: A single row of data

In relational theory, a tuple corresponds to a single row in a table, representing one complete record.

Which type of JOIN returns all rows from the left table and matching rows from the right table, with NULLs for unmatched right rows?

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.

Which Oracle object provides a reusable, auto-incrementing number generator often used to populate surrogate primary keys?

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.

Which property of a relational table means that rows have no inherent ordering?

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.