Ch8 Advanced SQL

Question 1

Get some examples of relational set operators

Answer 1

UNION, UNION ALL, INTERSECT, and MINUS

Question 2

What does UNION do?

Answer 2

Union combines rows from two or more queries without including duplicate rows.

Question 3

Give an example of a union relational set operator

Answer 3

SELECT emp_fname, emp_lname
FROM employee
UNION
SELECT emp_fname, emp_lname
FROM employee_1

Question 4

What does UNION ALL do?

Answer 4

UNION ALL produces a relation that retains duplicate rows. Union does not retain duplicate rows.

Question 5

What is the difference between union and union all?

Answer 5

Union includes duplicate rows union all does not

Question 6

What does the INTERSECT relational set operator do?

Answer 6

INTERSECT combines rows from two queries, returning only the rows that appear in both sets

Question 7

Relational set operators are only useful when _______

Answer 7

There are two or more tables with an identical list of attributes.

Question 8

What does the minus relational set operator do?

Answer 8

Minus returns only the rows that appear in the first set but not second

Question 9

How many rows in a table?

Answer 9

SELECT COUNT (*) FROM table name

Question 10

What is the difference between Group by and order by

Answer 10

Group by is for rows order by is for columns