6. Before any changes to database structure are attempted one should first:

A. clearly understand the current structure and contents of the database only.
B. test any changes on a test database only.
C. create a complete backup of the operational database only.
D. All of the above should be done.

7. Which of the following modifications may not succeed?

A. Changing a column data type from char to date
B. Changing a column data type from numeric to char
C. Both of the above actions should succeed.
D. Neither of the above actions will succeed.

8. How can you find rows that do not match some specified condition?

A. EXISTS
B. Double use of NOT EXISTS
C. NOT EXISTS
D. None of the above is correct.

9. A regular subquery can be processed:

A. from the top down.
B. from the bottom up.
C. by nesting.
D. None of the above is correct.

10. What SQL command can be used to add columns to a table?

A. MODIFY TABLE TableName ADD COLUMN ColumnName
B. MODIFY TABLE TableName ADD ColumnName
C. ALTER TABLE TableName ADD COLUMN ColumnName
D. ALTER TABLE TableName ADD ColumnName