1Z0-006 Fundamental Database Concepts 5

Question 1

What is the purpose of the ROLLBACK command in SQL?

Accepted Answer

To undo all changes made since the last COMMIT

Answer

ROLLBACK undoes all data modifications made during the current transaction, restoring the database to its state at the last COMMIT or SAVEPOINT.

Question 2

In First Normal Form (1NF), what requirement must be met?

Accepted Answer

Each column must contain atomic (indivisible) values with no repeating groups

Answer

1NF requires that each table cell contain a single, indivisible value and that there are no repeating groups or arrays within a row.

Question 3

Which SQL aggregate function counts only non-NULL values in a column?

Accepted Answer

COUNT(column_name)

Answer

COUNT(column_name) counts only non-NULL values in the specified column, while COUNT(*) counts all rows including those with NULLs.

Question 4

What is a database index, and what is its primary trade-off?

Accepted Answer

A data structure that speeds up reads; trade-off is slower writes and extra storage

Answer

An index speeds up SELECT queries by providing fast data lookup paths, but it slows down INSERT, UPDATE, and DELETE operations because the index must also be maintained.

Question 5

What does 'referential integrity' mean in a relational database?

Accepted Answer

Foreign key values must match existing primary key values in the referenced table or be NULL

Answer

Referential integrity ensures that a foreign key value in a child table must either match an existing primary key value in the parent table or be NULL.

(1Z0-006) Oracle Database Foundations Associate Practice Test

(1Z0-006) Oracle Database Foundations Associate Practice Test

1Z0-006 Fundamental Database Concepts 5