Question 1

What does the GROUP BY clause do in SQL?

Accepted Answer

It groups rows that have the same values in specified columns into summary rows.

Answer

It fetches unique values from a column.

Answer

It sorts the results of a query in ascending or descending order.

Answer

It combines two tables based on a common column.

Question 2

Which SQL query correctly identifies the car registration numbers that were not used between '2018-01-01' and '2018-01-15'?

Accepted Answer

SELECT rendszam FROM autok WHERE rendszam NOT IN (SELECT rendszam FROM utak WHERE datum BETWEEN '2018-01-01' AND '2018-01-15');

Answer

SELECT rendszam FROM autok WHERE rendszam <> (SELECT rendszam FROM utak WHERE datum BETWEEN '2018-01-01' AND '2018-01-15');

Answer

SELECT rendszam FROM autok WHERE rendszam IN (SELECT rendszam FROM utak WHERE datum BETWEEN '2018-01-01' AND '2018-01-15');

Answer

SELECT rendszam FROM autok WHERE rendszam NOT IN (SELECT rendszam FROM utak WHERE datum NOT BETWEEN '2018-01-01' AND '2018-01-15');

Question 3

What is the purpose of the INSERT statement shown in the text?

Accepted Answer

To add a new record to the 'vezetok' table.

Answer

To create the 'vezetok' table.

Answer

To update an existing record in the 'vezetok' table.

Answer

To delete a record from the 'vezetok' table.

Question 4

In the relation defined, which statement about the 'UTAK' table is true?

Accepted Answer

The 'datum' is part of the primary key of the 'UTAK' table.

Answer

The 'datum' column can have duplicate values.

Answer

The 'UTAK' table has multiple primary keys.

Answer

The 'datum' column must be unique across all records.

Question 5

What does the SQL statement 'DELETE FROM vezetok WHERE vkod=1;' do?

Accepted Answer

It attempts to delete the record from the 'vezetok' table where the 'vkod' is 1.

Answer

It updates the 'vkod' of the record in the 'vezetok' table to 1.

Answer

It creates a new record in the 'vezetok' table with 'vkod' 1.

Answer

It selects the record from the 'vezetok' table where the 'vkod' is 1.

Question 6

Which SQL query returns the dates on which only Ford type cars were used?

Accepted Answer

SELECT DISTINCT datum FROM utak INNER JOIN autok ON utak.rendszam=autok.rendszam WHERE tipus='Ford';

Answer

SELECT DISTINCT datum FROM utak INNER JOIN autok ON utak.rendszam=autok.rendszam WHERE tipus<>'Ford';

Answer

SELECT datum FROM utak INNER JOIN autok ON utak.rendszam=autok.rendszam;

Answer

SELECT datum FROM utak INNER JOIN autok ON utak.rendszam=autok.rendszam WHERE tipus<>'Ford';

Question 7

What does the statement 'UPDATE Autok SET afogy=afogy*1.1 WHERE (kor>10 AND szin='Piros') OR (kor<5 AND afogy<8);' accomplish?

Accepted Answer

It increases the 'afogy' field by 10% for specified conditions.

Answer

It deletes the records matching the conditions.

Answer

It selects records based on conditions.

Answer

It sets the 'afogy' field to a value of 10%.

Question 8

Which SQL query correctly shows the maximum 'vezeto' value?

Accepted Answer

SELECT MAX(vezeto) FROM vezetok;

Answer

SELECT COUNT(vezeto) FROM vezetok;

Answer

SELECT vezeto FROM vezetok;

Answer

SELECT MIN(vezeto) FROM vezetok;

Question 9

What does it mean if a foreign key has ON DELETE CASCADE?

Accepted Answer

It means that if a record in the parent table is deleted, all related records in the child table will also be deleted.

Answer

It enforces uniqueness in the child table.

Answer

It restricts deletion of records in the parent table if related records exist in the child table.

Answer

It allows multiple related records in the child table to refer to one record in the parent table.

Question 10

Which SQL command is used for creating a new table?

Accepted Answer

CREATE TABLE

Answer

UPDATE

Answer

ALTER TABLE

Answer

INSERT INTO

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