Databases & SQL worksheet with answers

Which SQL statement retrieves data from a table?

1. AUPDATE
2. BINSERT
3. CSELECT
4. DCREATE

Which SQL statement adds new rows to a table?

1. AUPDATE
2. BSELECT
3. CALTER
4. DINSERT

What is a candidate key?

1. AA set of columns shared between two tables to link their rows
2. BA minimal set of columns that uniquely identifies each row
3. CA column that is waiting to become a foreign key
4. DAny column that contains NULL values

What does the "A" in ACID stand for?

1. AAggregation
2. BAvailability
3. CAccuracy
4. DAtomicity

Why are indexes created on columns?

1. ATo save disk space
2. BTo prevent NULL values
3. CTo make inserts and updates faster on those columns
4. DTo speed up searches and joins on those columns

Why can a table have only one clustered index?

1. AThe SQL standard forbids more than one index on a table
2. BClustered indexes use too much memory
3. CClustered indexes can only be on the primary key
4. DThe rows can be stored physically in only one order

What does SELECT name, dept, AVG(salary) OVER (PARTITION BY dept) FROM emp return?

1. AOne row per department with its average salary
2. BAn error because name is not in a GROUP BY
3. COnly employees who earn more than their department average
4. DEvery employee row together with the average salary of their department

What does a FULL OUTER JOIN return?

1. AOnly matching rows
2. BOnly unmatched rows
3. CThe Cartesian product, pairing each row of one table with every row of the other
4. DAll rows from both tables, matched where possible and NULL-filled otherwise