SQL Fundamentals final test: 25 free questions

Q1 / 25

In ROUND(total, 2), why does 2 control the requested decimal places?

1. AThe largest argument always controls precision
2. BNumeric literals are matched by value rather than by position or order
3. CROUND reads arguments from right to left
4. DPositional arguments match parameters in their listed order

Q2 / 25

If T1 RIGHT OUTER JOIN T2 finds no match in T1 for a row in T2, what is the result?

1. AThe row from T2 is excluded from the final result set
2. BThe row from T2 is returned with NULL values for all columns of T1
3. CThe row from T2 is paired with the last valid row from T1
4. DThe query fails due to a foreign key violation

Q3 / 25

A table gives `status` a default of `draft`. An INSERT supplies only `sku` and `name`. What row is created?

1. AA row with no status column
2. BTwo rows, one for each supplied value
3. CA complete row whose status is draft
4. DNo row, because every column must be named

Q4 / 25

Why does the order of the input queries matter when using the EXCEPT operation?

1. AEXCEPT keeps first-only rows, so swapping inputs changes which differences remain
2. BBecause EXCEPT requires the query with more columns to be written first to determine the output shape
3. CBecause EXCEPT removes duplicates only from the first query, leaving duplicates in the second intact
4. DEXCEPT sorts using the first key

Q5 / 25

What does the token '2030-01-15' prove by itself?

1. AIt is a DATE value automatically in every SQL engine without a cast
2. BIt is text until a type or context gives it date intent
3. CIt is an identifier named 2030-01-15
4. DIt includes a time zone

Q6 / 25

The command ALTER TABLE tracks RENAME COLUMN name TO title runs on the stored tracks. What happens to the six stored titles?

1. ANothing changes; the six titles are the same
2. BThey are copied into the other columns
3. CThey move to a new column and the old one stays
4. DThey are cleared, so title starts empty

Q7 / 25

One side of an equality comparison is NULL. What does the comparison return?

1. ANULL, meaning unknown
2. BA plain false
3. CAn error, because null cannot be compared
4. DTrue, because both sides are comparable

Q8 / 25

The tracks table holds seven rows, and exactly two of them sit on album 1. Which subquery returns exactly one row, so it is safe in a place that expects a single value?

1. ASELECT max(milliseconds) FROM tracks
2. BSELECT name, milliseconds FROM tracks
3. CSELECT milliseconds FROM tracks
4. DSELECT milliseconds FROM tracks WHERE album_id = 1

Q9 / 25

Why does a CROSS JOIN not require an ON condition?

1. ABecause the WHERE clause is strictly required instead of ON
2. BBecause it returns every possible row pair and does not filter the pairs
3. CBecause it automatically joins on columns that have identical names
4. DBecause the database infers the condition from the primary keys

Q10 / 25

Which window function assigns the numbers 1, 2, 3, and so on to the rows of a partition, guaranteeing a unique number even for tied rows?

1. Arank
2. Blag
3. Cdense_rank
4. Drow_number

Q11 / 25

A `line_total` column must always equal `unit_price` multiplied by `quantity` for its own row, even after the row changes. Which definition gives that?

1. A`DEFAULT 0`, with the real total written in by hand later
2. BA default of price times quantity, applied once at insert time
3. CA generated column computed from the price and quantity of its row
4. DNo clause at all, leaving the total to the program that inserts

Q12 / 25

The invoices from the third of January to the end of January are wanted, and the invoice of the first of February has to stay out. Which condition does that?

1. Ainvoice_date BETWEEN '2026-01-03' AND '2026-02-01'
2. Binvoice_date >= '2026-01-03' AND invoice_date <= '2026-02-01'
3. Cinvoice_date > '2026-01-03' AND invoice_date <= '2026-02-01'
4. Dinvoice_date >= '2026-01-03' AND invoice_date < '2026-02-01'

Q13 / 25

One UPDATE must set a product's price to 3.49 and its status to live. Which SET clause does both?

1. ASET price = 3.49 AND status = 'live'
2. BSET (price = 3.49, status = 'live')
3. CSET price, status = 3.49, 'live'
4. DSET price = 3.49, status = 'live'

Q14 / 25

A named step called customer_totals groups invoices and returns customer_id and spent. The main query reads only `FROM customer_totals`, uses WHERE total >= 10, and fails. Why?

1. Acustomer_totals returns no column called total
2. BThe main query has to repeat the GROUP BY of the step
3. CA WITH clause cannot be followed by a WHERE clause
4. DA total can be compared inside the step that adds it

Q15 / 25

The `customers` table declares `customer_id` as its primary key. A developer then runs `CREATE UNIQUE INDEX customers_id_idx ON customers (customer_id);`. Which rule does the table gain?

1. ANo new rule; duplicates were already refused
2. BTwo rows may now share a customer_id
3. CThe customer_id column may now hold a null
4. DOnly the newest rows are checked for duplicates

Q16 / 25

Query A returns 10 distinct rows, Query B returns 5 distinct rows, and exactly 3 complete rows are shared. How many rows will Query A UNION ALL Query B return?

1. A3 rows
2. B15 rows
3. C12 rows
4. D10 rows

Q17 / 25

A department report must total salaries for active employees and return only departments whose resulting total exceeds 5000. Which query structure satisfies both requirements?

1. ATest the total in WHERE, group by department, then filter active rows in HAVING
2. BFilter active rows in WHERE, group by department, then test the total in HAVING
3. CGroup all rows by department, then test active status and the total together in WHERE
4. DFilter active rows in HAVING, then calculate each department total in WHERE

Q18 / 25

The team plans to drop `composer` from `songs`. The view `credits` selects `track_id` and `composer`; the view `hits` selects only `track_id` and `title`. Which view definition has to be dealt with as part of this migration?

1. ANeither, the database rewrites view text
2. Bcredits, because its text names composer
3. CBoth, since both read the same table
4. Dhits, because it was created first

Q19 / 25

The six track names are For Those About To Rock, Fast As a Shark, Restless and Wild, Princess of the Dawn, Let There Be Rock and Walk On Water. Which pattern keeps exactly one of them?

1. A'Fast As _ Shark'
2. B'F%'
3. C'%s%'
4. D'%Rock'

Q20 / 25

Inside one transaction, track 1 is repriced at 1.09. A savepoint named step_one follows. Track 2 is repriced at 1.09. The next line runs RELEASE SAVEPOINT step_one. Track 3 is repriced at 1.09, and the work is committed. Which prices are 1.09 at the end?

1. AOnly track 3 costs 1.09
2. BNone of the five tracks costs 1.09
3. COnly tracks 1 and 3 cost 1.09
4. DTracks 1, 2 and 3 all cost 1.09

Q21 / 25

A ledger needs four decimal places and exact sums and equality checks. Which type choice expresses that intent?

1. AAn integer with no documented scaling rule
2. BA character type because digits can be compared reliably as text
3. CUse an exact decimal type with enough precision and scale
4. DA floating-point type because it stores approximations

Q22 / 25

A query filters artists with EXISTS (SELECT 1 FROM albums b WHERE b.artist_id = a.artist_id). For AC/DC the inner query returns three album rows. What is the value of that test?

1. ATrue only if the three rows hold equal values
2. BFalse, because the test needs exactly one row
3. CUnknown, because the inner query selects a constant
4. DTrue, because at least one row came back

Q23 / 25

The store wants at most one invoice per customer per day, while a customer may still buy on many days and several customers may buy on the same day. Which rule states that?

1. AOne unique index on each of the two columns separately
2. BA unique index on customer_id
3. CA unique index on customer_id and invoice_date together
4. DA unique index on invoice_date

Q24 / 25

Which structural requirement must two queries meet before PostgreSQL combines them with a UNION?

1. AThey must query tables that share an explicitly defined foreign key relationship
2. BThe same column count, with compatible data types in each matching position
3. CThey must return columns that have the exact same names in both queries
4. DThey must both contain a WHERE clause to filter the results before combining

Q25 / 25

A table records sales with a year, a region, and an amount. You need to group the sales to find the total amount per region within each year. Which GROUP BY clause forms groups at this intended grain?

1. AGROUP BY year, which merges all regions within each year
2. BGROUP BY region, which merges all years within each region
3. CGROUP BY amount, which groups equal sales values together
4. DGROUP BY year, region