Databases & SQL worksheet with answers

Which SQL statement changes values in rows that already exist?

1. AREPLACE COLUMN
2. BMODIFY
3. CUPDATE
4. DINSERT

What is an entity-relationship (ER) diagram used for?

1. AModelling entities, their attributes and relationships when designing a database
2. BListing the users of a database
3. CMeasuring database performance
4. DShowing how a query is executed

In the relational model, what is a row of a table called?

1. AA domain
2. BA tuple
3. CAn attribute
4. DA schema

What does SELECT COALESCE(phone, 'unknown') FROM customers return for a customer whose phone is NULL?

1. AAn empty string
2. BNULL
3. CAn error
4. D'unknown'

What does EXCEPT (called MINUS in Oracle) return?

1. ARows of the first query that do not appear in the second
2. BAll rows from both queries without duplicates
3. CRows that appear in both queries
4. DRows of the second query that do not appear in the first one

Why are indexes created on columns?

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

Which window function assigns 1, 2, 3, ... to rows within each partition without ties?

1. ACOUNT()
2. BRANK()
3. CDENSE_RANK()
4. DROW_NUMBER()

Two doctors on call each check that the other is still on call, then both sign off at the same time. Which anomaly can snapshot isolation still allow here?

1. AWrite skew
2. BNon-repeatable read within one transaction
3. CDirty read
4. DDirty write