Relational Database Concepts - Quiz Explanation

The answers you selected are indicated below, along with text that explains the correct answers.
 
1. Which of the following is likely to result from normalizing your data?
Please select the best answer.
  A. More tables are created.
  B. Fewer tables are created.
  C. The same number of tables are created.
  D. Depending on the situation, more or less tables can be created.
  The correct answer is A. Normalizing data ensures that data that is not part of the primary key does not repeat within the same table. That means it is broken into separate tables, increasing the total number of tables in the data set. B is incorrect because breaking data into separate tables will increase, not decrease, the total number of tables. C is incorrect because breaking data into separate tables will result in a net increase in the total number of tables. D is incorrect because normalizing your data always results in the creation of more tables.

2. What does a primary key define?
Please select the best answer.
  A. The relationship of data between two or more tables
  B. The quality of data in a table
  C. The columns that uniquely identify a row in a table
  D. The data that uniquely identifies a single column
  The correct answer is C. A primary key defines the columns that uniquely identify a row in a table. A is incorrect because it's referential integrity that defines the relationship of data between two or more tables. B is incorrect because it's data integrity that defines the quality of data in a table. D is incorrect because a primary key can define more than one column.

3. What kind of key would you use to define which values from the primary key in Table A are valid for a column in Table B?
Please select the best answer.
  A. Primary key
  B. Unique key
  C. Identity flag
  D. Foreign key
  The correct answer is D. You would use a foreign key to define which values from the primary key in Table A are valid for a column in Table B. (This is the same as enforcing referential integrity in Table B from a primary key in Table A.) A is incorrect because a primary key uniquely identifies rows in a table. B is incorrect because a unique key enforces unique values in a column. C is incorrect because an identity flag has nothing to do with a value in another table.

4. Which Transact-SQL fragment would you use to test a value in the Address column to see if it is null?
Please select the best answer.
  A. Where Address = NULL
  B. Where Address IS NOT NULL
  C. Where Address IS NULL
  D. Where Address = `'
  The correct answer is C. To test for a null value, use the IS NULL keywords. A is incorrect because you use = NULL to assign a null value, not to test for it. B is incorrect because you use the keywords NOT NULL to test whether a value is not null, not whether it is null. D is incorrect because you cannot test for a null value with an empty string.