Databases & SQL worksheet with answers

In a LIKE pattern, what does the % wildcard stand for?

1. AExactly one character in that position of the string
2. BThe end of the string
3. CAny sequence of zero or more characters
4. DAny single digit

Which keyword sorts the result of a query?

1. AORDER BY
2. BGROUP BY
3. CARRANGE
4. DSORT

What does UNION do with the results of two SELECT queries?

1. ACombines them into one result and removes duplicate rows
2. BKeeps only rows that appear in both
3. CJoins them side by side on a key
4. DKeeps only rows that appear in the first query but not the second

Students can take many courses and courses have many students. How is this modelled in tables?

1. AWith a foreign key column course_id in the students table pointing to courses
2. BWith a list of course ids stored in one column
3. CBy merging students and courses into one table
4. DWith a junction table holding foreign keys to both students and courses

A table stores the customer's address on every order row. Changing the address in one row but not in the others is an example of:

1. AAn insertion anomaly
2. BA phantom read
3. CAn update anomaly
4. DA deletion anomaly

In relational algebra, the selection operator (σ) corresponds to which SQL clause?

1. AGROUP BY
2. BSELECT list
3. CORDER BY
4. DWHERE

When is decomposing R into R1 and R2 guaranteed to be lossless?

1. AWhen R1 and R2 have the same number of columns
2. BWhen every attribute of R appears in both R1 and R2
3. CWhen R1 and R2 have no attributes in common
4. DWhen the common attributes of R1 and R2 form a superkey of R1 or of R2

What does SELECT day, SUM(amount) OVER (ORDER BY day) FROM sales compute?

1. AThe total of all amounts on every row
2. BThe average amount per day
3. COne row per day with that day's total only
4. DA running total of amount ordered by day