Multiple Choice Questions for SQL

My multiple choice questions are for the SQL lessons.

Question 1: SQL ‘UNION’

Which of the following SQL commands is used to combine the results of to queries so that all of the output of each query is present in the final result?

1. LEFT INNER JOIN
2. RIGHT JOIN
3. UNION
4. LEFT OUTER JOIN

Question 2: SQL ‘UNION’

In the aggregation portion of the lesson, we saw that avg can be used to get the mean of a set of values. What does the avg function return when called on the values 0.0, 1.0, 2.0, 3.0, and null?

1. An error
2. 1.2
3. 1.5
4. 2.0

The first distractor (‘an error’) is meant to catch the misconception that the avg function cannot be run on a set that includes null values. The second distractor (1.5) could be chosen if the student thinks that null values are ignored (i.e. (0.0+1.0+2.0+3.0)/4 = 1.5). The third distractor (2.0) might be chosen if the student thinks that both zeroes and null values are ignored in the avg function. The second answer (1.2) is correct.