Tag: databases

To answer this question, you need to understand the concept of a right outer join.

A right outer join returns all the rows from the right table (the table mentioned after the "RIGHT OUTER JOIN" keyword in the query) and the matching rows from the left table (the table mentioned before the "RIGHT OUTER JOIN" keyword). If there is no match between the tables, the left table will still return all its rows, but the columns from the right table will have NULL values.

So, in the scenario where there is NO match between the tables, the final result of a right outer join will be:

D. The left table will return ALL rows.

This is because the left table returns all its rows regardless of whether there is a match with the right table.

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• Wrong explanation

To answer this question, let's go through each option to understand why it is correct or incorrect:

Option A) Primary key constraint creates clustered index by default - This option is incorrect. While it is true that a primary key constraint creates an index by default, it does not necessarily create a clustered index. By default, a primary key constraint creates a unique nonclustered index. However, you can choose to create a clustered index on the primary key by specifying it explicitly.

Option B) Unique key constraint creates clustered index by default - This option is incorrect. A unique key constraint, like a primary key constraint, does not create a clustered index by default. It creates a unique nonclustered index. You can choose to create a clustered index on a unique key by specifying it explicitly.

Option C) Primary key constraint allows null values - This option is incorrect. A primary key constraint does not allow null values. It enforces the uniqueness of the key and requires that every value in the column(s) defined as the primary key be unique and not null.

Option D) Unique key constraint allows null values - This option is correct. A unique key constraint allows null values. While it enforces the uniqueness of the key, it allows for one null value in the column(s) defined as the unique key. However, it still enforces that all non-null values must be unique.

Based on the explanations above, the correct answer is A and D.

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• Wrong explanation

To answer this question, you need to understand the characteristics of metadata. Let's go through each option to understand why it is correct or incorrect:

Option A) Data about Data - This option is correct. Metadata refers to data about data, providing information about the characteristics and properties of the data.

Option B) Describes a data dictionary - This option is incorrect. While metadata can include information about a data dictionary, it is not the sole purpose of metadata. Metadata describes the data itself, including its structure, format, and relationships.

Option C) Self-describing - This option is correct. One of the characteristics of metadata is that it is self-describing. It contains information that allows users and systems to understand and interpret the data it describes.

Option D) Includes user data - This option is incorrect. User data is not considered metadata. Metadata focuses on providing information about the data, not the actual data itself.

The correct answer is D) Includes user data. This option is incorrect because user data is not considered metadata.

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• Wrong explanation