Multiple choice technology databases

For which two constraints does the Oracle Server implicitly create a unique index?

  1. Not null

  2. Primary key

  3. Foreign key

  4. Check

  5. Unique
Reveal answer Fill a bubble to check yourself
B,E Correct answer
Explanation

Oracle automatically creates a unique index to enforce PRIMARY KEY and UNIQUE constraints. This unique index ensures that duplicate values cannot be inserted. NOT NULL, FOREIGN KEY, and CHECK constraints do not require unique indexes for their enforcement - they use different mechanisms.

AI explanation

To answer this question, we need to understand the concept of constraints in a database and how they relate to indexes.

Constraints are rules that are applied to columns or tables in a database to enforce data integrity. They ensure that the data stored in the database follows certain rules or conditions.

An index, on the other hand, is a data structure that improves the speed of data retrieval operations on a database table. It allows for faster searching and sorting of data.

In Oracle Server, there are several types of constraints that can be defined on a table, including:

A. Not null - This constraint ensures that a column cannot have a null value. B. Primary key - This constraint ensures that a column or a combination of columns uniquely identifies each row in a table. It implicitly creates a unique index on the primary key column(s). C. Foreign key - This constraint ensures that values in a column (or a set of columns) of one table match the values in another table's primary key or unique key column(s). D. Check - This constraint ensures that the values in a column meet a specific condition or set of conditions. E. Unique - This constraint ensures that the values in a column (or a set of columns) are unique across all rows in a table. It implicitly creates a unique index on the unique constraint column(s).

Based on the given options, the two constraints for which the Oracle Server implicitly creates a unique index are:

B. Primary key - This constraint ensures that a column or combination of columns uniquely identifies each row in a table. The Oracle Server implicitly creates a unique index on the primary key column(s). E. Unique - This constraint ensures that the values in a column (or a set of columns) are unique across all rows in a table. The Oracle Server implicitly creates a unique index on the unique constraint column(s).

Therefore, the correct answer is B and E.

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