TI2: Quiz 7

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TI2: Quiz 7

Dataset of articles published in scientific journals

Which of the sets below are candidate keys for the given table?

A candidate key is a column or set of columns of a table that can uniquely identify any database record (row) without ambiguity.

{ID}

{ID,TR-ID}

{title}

{title,year,journal}

{ID,title,TR-ID}

{startpage,journal,issue}

Which of the SQL statements are invalid?

A valid statement is accepted by a standard SQL interpreter, whereas an invalid statement results in an error message.

1. SELECT * FROM Articles WHERE endpage - startpage > 10;

2. SELECT * FROM Articles WHERE endpage - startpage < 0;

3. SELECT SUM(title) FROM Articles;

4. SELECT AVG(year) FROM Articles WHERE title LIKE ’C%’;

5. SELECT COUNT(*) FROM Articles GROUP BY year;

6. SELECT year,COUNT(*) FROM Articles WHERE COUNT(*) > 10 GROUP BY year;

How many rows does this query return for the given table?

SELECT DISTINCT ID FROM Articles WHERE year < 2006;

2 rows

3 rows

4 rows

5 rows

Clear selection

If table A is on the left and table B is on the right, a right outer join will include in its answer ...

Only the rows for which the values of the two tables’ common attribute match exactly.

All the rows from Table A, with the corresponding detail of Table B for those rows for which the values of the two tables’ common attribute match exactly.

All the rows from Table B, with the corresponding detail of Table A for those rows for which the value of the two tables’ common attribute match exactly.

All rows from both Table A and Table B.

Clear selection

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