1. CS 3630 Database Design and Implementation

2. Project Phase II Assignment 8
Due Monday, April 10, by 5 PM

3. Aggregate Functions Produce a single value from a set
Examples: Max, Min, Sum, Avg, Count

4. Aggregate functions
Count
Max
Min
Sum
Avg …

5. SQL Aggregate Functions
// Max, Min, Avg, Sum
Select Max(price), Min(price), Avg(price)
From room;
Select Max(room_no), Min(room_no)
Select Avg(room_no), Sum(room_no)
// No!
// Room_No char(4)

6. Max/Min Dates Select Min(Date_From), Max(Date_To) From Booking;
Col Min(Date_From) Format a20 Heading 'Earlist Date_From'
Col Max(Date_To) Format a20 Heading 'Latest Date_To'
Select To_Char(Min(Date_From), 'Mon dd yyyy'),
To_Char(Max(Date_To), 'Mon dd yyyy')

7. Max/Min Dates col "Earliest Date from" format a20
col "Latest Date To" format a20
Select To_Char(Min(Date_From), 'Mon dd yyyy')
"Earliest Date from",
To_Char(Max(Date_To), 'Mon dd yyyy')
"Latest Date To"
From Booking;
-- Incorrect!
Select Min(To_Char(Date_From, 'Mon dd yyyy')),
Max(To_Char(Date_To, 'Mon dd yyyy'))

8. Aggregate Functions -- Count(*): number of all records
-- count(hotel_no): number of Hotel_No
-- Count(unique Hotel_No):
number of distinct Hotel_No
Select count(*), count(hotel_no),
count(unique hotel_no)
From room;
-- Does not count null values
select count(*), count(address)
From guest;

9. Aggregate Functions Select Avg(Price) From room; -- With Distinct
Select Avg(Distinct Price)

10. Aggregate Functions with Where
-- With where clause
-- Avg is applied after Where clause
Select Avg(Price)
From room
Where rtype = 'Family';
Where rtype = 'Single'
Where rtype = 'Double'

11. Aggregate Functions with Where
-- With where clause
-- Avg is applied after Where clause
Select 'Average Price of Family rooms: ',
Avg(Price)
From room
Where rtype = 'Family‘;
Select rtype, Avg(Price)
Where rtype = 'Family';
-- change rtype to Single, Double

12. One record for each group.
Group By Clause
Count, Avg
Select
Group By
Count, Avg
Count, Avg
One record for each group.

13. Group By Select Avg(Price) From room Group by rtype;
Select rtype, Avg(Price)

14. Group By Clause
For each hotel, display Hotel_No with the number of rooms.
Select Hotel_No, Count(*)
From Room
Group By Hotel_No;
Hotel_No
Room_No
Price
H01
R001 30
R002 35
H05
R003 40
R103 45
R101 50
Hotel_No
Room_No
Price
H01
R001 30
R002 35
R103 45
H05
R003 40
R101 50
Hotel_No
Count
H01 3
H05 2

15. What can be selected with Group By Clause
Can select Hotel_No, the group by field
Can select aggregate functions on any other fields such as Max(Room_No) or Avg(Price)
Hotel_No
Room_No
Price
H01
R001 30
R002 35
R103 45
H05
R003 40
R101 50
Hotel_No
Room_No
Price
H01
R001 30
R002 35
R103 45
H05
R003 40
R101 50
Hotel_No
Max(Room_No)
Avg(Price)
H01
R103
36.67
H05
R101 45

16. What CANNOT be selected with Group By Clause
Cannot select no group by fields such as Room_No or Price
ORA-00979: not a GROUP BY expression
Hotel_No
Room_No
Price
H01
R001 30
R002 35
R103 45
H05
R003 40
R101 50
Hotel_No
Room_No
Price
H01
R001 30
R002 35
R103 45
H05
R003 40
R101 50
Hotel_No
Room_No
Price
H01 ?
H05

17. Group By Clause ? Select Group By ? ? One record for each group!
What can be selected?
Aggregate functions
Group by fields

18. Group By One Record for each group
Select Hotel_no, Count(*), Max(Price)
From Room
Group by Hotel_No;
Select Hotel_no, Room_No, rtype,
Price
-- not a Group By expression

19. Group by more than one field
Select Hotel_No, rtype, Max(Price)
From Room
Group By Hotel_no, rtype;

20. Order after Group by Group By Select Hotel_no, Count(*), Max(Price)
From Room
Group by Hotel_No
Order by Count(*);

21. Group By Clause ? Select Group By ? ?
What if we don’t want all groups?
Having on groups
Where on records

22. Group By Having to select groups Select Hotel_no, Count(*), Max(Price)
From Room
Group by Hotel_No
Having Count(*) > 20;

23. Group By Where before Group by to select records
Having after Group by to select groups
Let’s do it in 4 steps:
From, Where, Group By, Having
Select Hotel_no, Count(*), Max(Price)
From Room
Where rtype = 'Single'
Group by Hotel_No
Having Max(Price) < 100

24. Group By Where before Group by Having after Group by Order by last
Select Hotel_no, Count(*), Max(Price)
From Room
Where rtype in ('Double', 'Single')
Group by Hotel_No
Having Count(*) > 50
Order by Count(*);

25. Group By Clause Execution Order Where (condition on records) Group by
Having (condition on groups)
Order by
(Select)

26. Command Prompt Prompt Prompt 9.
Prompt For each hotel that has more than
Prompt one Single room, list hotel number
Prompt with number of Single rooms the hotel
Prompt has and the highest price of
Prompt such rooms of the hotel.
Select Hotel_no, Count(*), Max(Price)
From Room
Where rtype = 'Single'
Group by Hotel_No
Having Count(*) > 1
Order by Count(*);

27. Assignment 8 Due Monday, April 10 Should work for any table instance
Run against my tables
Should insert more records to test
(Don’t include insert commands!)
Example
Quiz 3
Hands-On
Wednesday, April 7
Create Script file to
Drop tables
Create tables
Column/Table constraints
Insert records