1. Structured Query Language (II) (結構化查詢語言)
SQL
Structured Query Language (II)
(結構化查詢語言)
2018/12/1

2. SQL query – Grouping SELECT ...... FROM ...... WHERE condition
GROUP BY groupexpr
[HAVING requirement]
Group functions:
COUNT( ), SUM( ), AVG( ), MAX( ), MIN( )
– groupexpr specifies the related rows to be grouped as one entry. Usually it is a column.
– WHERE condition specifies the condition of individual rows before the rows are group. HAVING requirement specifies the condition involving the whole group.
2018/12/1

3. Example field type width contents id numeric 4 student id number
Table: stud
field type width contents
id numeric student id number
name character name
dob date date of birth
sex character sex: M / F
class character class
hcode character house code: R, Y, B, G
dcode character district code
remission logical fee remission (學費減免)
mtest numeric Math test score
2018/12/1

4. 1A 1A 1B 1C 1B 1C Group By Class COUNT( ) COUNT( ) COUNT( )
e.g.1 List the number of students of each class.
Group By Class
Stud
class 1A 1B 1C 1A 1A 1B 1C
COUNT( )
COUNT( ) 1B
COUNT( ) 1C
2018/12/1

5. Grouping SELECT class, COUNT(*) FROM stud GROUP BY class
eg. 1 List the number of students of each class.
SELECT class, COUNT(*)
FROM stud
GROUP BY class
Result
2018/12/1

6. Grouping SELECT class, Round(AVG(mtest),2) FROM stud GROUP BY class
e.g. 2 List the average Math test score of each class.
SELECT class, Round(AVG(mtest),2)
FROM stud
GROUP BY class
Result
2018/12/1

7. Grouping SELECT dcode, COUNT(*) FROM stud WHERE sex=‘F’ GROUP BY dcode
e.g. 3 List the number of girls of each district.
SELECT dcode, COUNT(*)
FROM stud
WHERE sex=‘F’
GROUP BY dcode
Result
2018/12/1

8. Grouping SELECT MAX(mtest), MIN(mtest), dcode FROM stud
e.g. 4 List the max. and min. test score of Form 1 students of each district.
SELECT MAX(mtest), MIN(mtest), dcode
FROM stud
WHERE class LIKE ‘1_’
GROUP BY dcode
Result
2018/12/1

9. Grouping SELECT AVG(mtest), class FROM stud WHERE sex=‘M’
e.g. 5 List the average Math test score of the boys in each class. The list should not contain class with less than 3 boys.
SELECT AVG(mtest), class
FROM stud
WHERE sex=‘M’
GROUP BY class
HAVING COUNT(*) >= 3
Result
2018/12/1

10. Grouping
2018/12/1

11. Multiple Tables – Join by Columns:
SQL provides a convenient operation to retrieve information from multiple tables.
This operation is called
Join (接合)
The join operation will combine the
tables into one large table by
columns (欄)
An Inner Join is a join operation that joins two tables by their
common column (共通欄)
It combines records from two tables only if the
values of the joined fields meet a specified
condition.
The join operation is also called
Equi-Join
2018/12/1

12. 1. Inner Join (內接合) – Syntax
SELECT a.comcol, a.col1, b.col2, expr1, expr2 ;
FROM table1 a, table2 b ;
WHERE a.comcol = b.comcol and filterCondition
2018/12/1

13. Table : d_play_list_items Table : d_track_listings
1. Equi-Join / Inner Join
Table : d_play_list_items
Table : d_track_listings
2018/12/1

14. Example: Music Instrument learnt by students
Table: stud
field type width contents
id numeric student id number
name character name
dob date date of birth
sex character sex: M / F
class character class
hcode character house code: R, Y, B, G
dcode character district code
remission logical fee remission (學費減免)
mtest numeric Math test score
Table: music
field type width contents
id numeric student id number
type character type of the music instrument
2018/12/1
Join by The common field: id

15. they learn. (Inner Join)
eg.1 Make a list of students and the instruments
they learn. (Inner Join)
Student
9801 id
name
class
Music id
9801
type
Same id
Join
9801
Product id
name
class
type
2018/12/1

16. they learn. (Inner Join)
eg.1 Make a list of students and the instruments
they learn. (Inner Join)
SELECT s.class, s.name, s.id, m.type
FROM stud s, music m
WHERE s.id=m.id ORDER BY class, name
Result
2018/12/1

17. (2) Condition: m.type="Piano" (3) GROUP BY class
eg.2 Find the number of students learning piano
in each class.
Three Parts :
(1) Inner Join.
(2) Condition: m.type="Piano"
(3) GROUP BY class
2018/12/1

18. in each class. eg.2 Find the number of students learning piano Join
Music
Student
Join
Product
Condition
m.type= "Piano"
Group By
class
2018/12/1

19. SELECT s.class, COUNT(*) FROM stud s, music m
eg.2 Find the number of students learning piano
in each class.
SELECT s.class, COUNT(*)
FROM stud s, music m
WHERE s.id=m.id AND m.type=‘Piano’
GROUP BY class ORDER BY class
Result
2018/12/1

20. Other Examples of Inner Join
In a DBMS of a Musical Instrumental Co. , 3 tables are used:
Salorder m m
Client 1 1
Salstaff
2018/12/1

21. SELECT O.order_no, C.client, C.name FROM salOrder O, Client C
e.g1 Display the names of the contact person and client, corresponding to the same order. (Two Tables)
SELECT O.order_no, C.client, C.name
FROM salOrder O, Client C
WHERE O.client_id =C.client_id
Result
2018/12/1

22. SELECT O.order_no, S.name as salesperson, O.order_date
e.g.2 Display the sales orders made between May and June , with
the corresponding salespersons in the same cursor (list by date).
SELECT O.order_no, S.name as salesperson, O.order_date
FROM salOrder O, salStaff S WHERE O.staff_id=S.staff_id
and order_date between '1-5月-2006' and '30-6月-2006'
ORDER BY 3
Result
2018/12/1

23. e.g.3 Display the names of the contact person , client and the
salesperson corresponding to the same sales order. (3 Tables)
SELECT O.order_no, C.client, C.name as contact, S.name as salesperson
FROM salOrder O, client C, salStaff S
WHERE O.staff_id=S.staff_id and O.client_id=C.client_id
From salOrder
From client
From client
From salStaff
Result
2018/12/1

24. 2. Nonequi-Join SELECT d_packages.code, d_events.cost
FROM d_packages, d_events
WHERE d_events.cost
BETWEEN
d_packages.low_range
AND d_packages.high_range
2018/12/1

25. 3. Outer Join (外接合)
An Outer Join is a join operation that selects all the rows from the first table including those match and those do not match the rows in the second table.
Those not matching join condition will be a
(-) value.
null
2018/12/1

26. 3. Left Outer Join – Syntax
SELECT a.comcol, a.col1, b.col2, expr1, expr2 ;
FROM table1 a
LEFT OUTER JOIN table2 b ;
ON a.comcol = b.comcol
WHERE filterCondition
ORDER BY …
SELECT a.comcol, a.col1, b.col2, expr1, expr2 ;
FROM table1 a, table2 b ;
WHERE a.comcol = b.comcol (+)
and filterCondition
ORDER BY …
(+) sign indicates the table has missing data.
2018/12/1

27. Inner Join Outer Join No Match
eg. Make a checking list of students and the instruments they learn. The list should also contain the students without an instrument.
(Outer Join)
Inner Join
Outer Join
No Match
2018/12/1

28. eg. Make a checking list of students and the. instruments they learn
eg. Make a checking list of students and the instruments they learn. The list should also contain the students without an instrument.
(Outer Join)
SELECT s.class, s.name, s.id, m.type
FROM stud s
LEFT OUTER JOIN music m
ON s.id=m.id ORDER BY 1, 2
FROM stud s, music m
where s.id=m.id(+) order by 1,2
Result
Outer Join
empty
2018/12/1

29. Select e.employee_id, e.last_name, d.department_name
3. Outer Join
Null value
Select e.employee_id, e.last_name, d.department_name
From employees e, departments d
Where e.department_id=d.department_id(+)
2018/12/1

30. 3. Outer Join (Right Outer Join)
Select e.last_name, e.department_id, d.department_name
From employees e, departments d
Where e.department_id (+) =d.department_id
The right outer join would return all department IDs and department names even if no employees were assigned to them.
2018/12/1

31. 3. Outer Join (Full Outer Join)
The results set of a full outer join includes all rows in both tables even if there is no match in the other table.
Remember, in this form of an outer join, it was not possible to put a (+) on both sides of the WHERE clause.
2018/12/1

32. 4. Cartesian Product / Cross Join
1. Select * from stud
2. Select * from music
3. Select * from stud, music
4. Select * from stud cross join music
How many records before and after the join?
2018/12/1

33. Select worker.last_name ||' works for '|| manager.last_name
5. SELF JOIN
Table : Employees
Select worker.last_name
||' works for '|| manager.last_name
From employees worker,
employees manager
Where worker.manager_id = manager.employee_id
2018/12/1

34. 6. NATURAL JOIN
A natural join is based on all columns in the two tables that have the same name and selects rows from the two tables that have equal values in all matched columns. It is possible to join the tables without having to explicitly specify the columns in the corresponding table. However, the names and data types in both columns must be the same.
Table : d_track_listings
Table : d_play_list_items
SELECT event_id, song_id, cd_number
FROM d_play_list_items
NATURAL JOIN d_track_listings
WHERE event_id = 105
2018/12/1

35. JOIN (USING Clause)
2018/12/1

36. JOIN (ON Clause)
2018/12/1

37. There are two types of subqueries:
-Single-row subqueries that use single-row operators (>, =, >=, < <>, <=)
and return only one row from the inner query
e.g. SELECT name from stud where mtest <= (select avg(mtest) from stud)
Multiple-row subqueries that use multiple-row operators (IN, ANY, ALL)
and return more than one row from the inner query
2018/12/1

38. Subqueries - IN IN (= ANY) NOT IN (<> ALL) SELECT title, year
FROM d_cds
WHERE year IN
(SELECT year
WHERE cd_number
< 94)
IN (= ANY)
NOT IN (<> ALL)
2018/12/1

39. Subqueries - ANY SELECT title, producer, year FROM d_cds
WHERE year = ANY
(SELECT year
WHERE producer = 'The Music Man')
2018/12/1

40. Subqueries - ALL SELECT title, producer,year FROM d_cds
WHERE year > ALL
(SELECT year
WHERE producer = 'The Music Man')
2018/12/1

41. Tutorial Exercise Time
2018/12/1

42. The End
2018/12/1

43. The union (數據庫聯合) of A and B (AB)
Lesson Review
Two Tables with same structure: Table A and Table B
What is Union in Multiple Tables?
The union (數據庫聯合) of A and B (AB)
A table containing all the rows from A and B. A B
2018/12/1

44. Real Case: Bridge Club & Chess Club
Consider the members of the Bridge Club and the Chess Club. The two database files have the same structure:
Union
List members of either clubs
order by class, name
2018/12/1

45. The intersection (數據庫相交) of A and B (AB)
Lesson Review
Two Tables with same structure: Table A and Table B
What is Intersection in Multiple Tables?
The intersection (數據庫相交) of A and B (AB)
A table containing only rows that appear in both A and B. A B
2018/12/1

46. Real Case: Bridge Club & Chess Club
Consider the members of the Bridge Club and the Chess Club. The two database files have the same structure:
Intersection
Members of both clubs
2018/12/1

47. The difference (數據庫差分) of A and B (A–B)
Lesson Review
Two Tables with same structure: Table A and Table B
What is Difference in Multiple Tables?
The difference (數據庫差分) of A and B (A–B)
A table containing rows that appear in A but not in B. A B
2018/12/1

48. Real Case: Bridge Club & Chess Club
Consider the members of the Bridge Club and the Chess Club. The two database files have the same structure:
Difference
Members of Bridge Club
but Not Chess Club
2018/12/1

49. Lesson Review 1. Union Syntax of SQL
SELECT FROM WHERE ;
UNION ;
SELECT FROM WHERE
2018/12/1

50. Lesson Review 2. Intersection Syntax of SQL
SELECT FROM table1 ;
WHERE col IN ( SELECT col FROM table2 )
Note: col stands for one of the common column in the two tables
2018/12/1

51. Lesson Review 3. Difference Syntax of SQL SELECT ...... FROM table1 ;
WHERE col NOT IN ( SELECT col FROM table2 )
Note: col stands for one of the common column in the two tables
2018/12/1

52. This Lesson
eg. 9 List the students who have not yet chosen an instrument. (No match)
Student
9801 id
name
class
Music id
type
No match
2018/12/1

53. WHERE id NOT IN ( SELECT id FROM music ) ;
eg. 9 List the students who have not yet chosen an
instrument. No match (Difference)
SELECT class, name, id FROM student ;
WHERE id NOT IN ( SELECT id FROM music ) ;
ORDER BY class, name
Result
2018/12/1