1. CS122 Using Relational Databases and SQL
7/29/2018
CS122 Using Relational Databases and SQL
4. Subqueries and joins
Randy Moss
Department of Computer Science
California State University, Los Angeles

2. Outline Subqueries Joining tables Subqueries in the WHERE clause
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Outline
Subqueries
Subqueries in the WHERE clause
Subqueries with IN, ALL & ANY
Joining tables
Learn how SQL joins tables
Join tables using an Equi Join
Join tables using an Inner Join
4. Subqueries and joins CS122_W2014

3. Sub-Queries A query within a query Sub-query placed in parentheses
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Sub-Queries
A query within a query
Sub-query placed in parentheses
Sub-queries can be placed in
WHERE clause
HAVING clause
SELECT clause
FROM clause
4. Subqueries and joins CS122_W2014

4. Sub-Queries examples (1)
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Sub-Queries examples (1)
List the name of the oldest member
Find the earliest birthday ( )
Select min(birthday)
From Members
Find the member whose birthday is ‘ ’
Select firstname, lastname
Where birthday = ‘ ’
4. Subqueries and joins CS122_W2014

5. Sub-Queries examples (1)
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Sub-Queries examples (1)
Combine the two queries
SELECT firstname, lastname
FROM Members
WHERE birthday = (SELECT Min(birthday)
FROM Members )
4. Subqueries and joins CS122_W2014

6. Outer query looks for records with Birthday matching Sub-Query value
Sub-Query Example (1)
Outer query looks for records with Birthday matching Sub-Query value
Select Lastname, Firstname From Members Where Birthday = (Select Min(Birthday) From Members)
Sub-Query returns
Query returns
Lastname Firstname
Wong Tony

7. Sub-Queries examples (2)
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Sub-Queries examples (2)
List all track titles and lengths of all tracks whose length is longer than the average of all track lengths
Find the average track lenghths (276.08)
SELECT Avg(lengthseconds) FROM Tracks
Find the all track titles and lengths of all tracks whose length is greater than
SELECT tracktitle, lengthseconds
FROM Tracks
WHERE lengthseconds >
4. Subqueries and joins CS122_W2014

8. Sub-Queries examples (2)
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Sub-Queries examples (2)
Combine the two queries
SELECT tracktitle, lengthseconds
FROM Tracks
WHERE lengthseconds > ( SELECT Avg(lengthseconds) FROM Tracks )
4. Subqueries and joins CS122_W2014

9. 7/29/2018
Sub-Queries using IN
Report the name of all artists who have recorded a title
SELECT artistName
FROM Artists
WHERE artistID IN (SELECT artistID
FROM Titles)
4. Subqueries and joins CS122_W2014

10. ALL & ANY Used with Sub-Queries
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ALL & ANY
Used with Sub-Queries
Can be used with greater than and less than tests
If using ANY, then comparison will be true if it satisfies any value produced by the sub-query
SOME is functionally equivalent to ANY
If using ALL, then comparison will be true if it satisfies all values produced by the sub-query.
4. Subqueries and joins CS122_W2014

11. ALL example
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List the name, region, and birthday of every member who is older than all of the members in Georgia
Select Birthday From Members Where Region='GA'
Birthday
Select Lastname, Firstname, Region, Birthday From Members Where Birthday < ALL(Select Birthday From Members Where Region='GA')
Lastname Firstname Region Birthday
Ranier Brian ONT
Kale Caroline VA
Wong Tony ONT
Cleaver Vic VT
4. Subqueries and joins CS122_W2014

12. ANY example WHERE region = 'GA' )
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ANY example
List the name, region, and birthday of every member who is older than any of the members in Georgia
SELECT lastname, firstname, region, birthday
FROM Members
WHERE birthday < ANY (SELECT birthday
FROM Members
WHERE region = 'GA' )
4. Subqueries and joins CS122_W2014

13. 7/29/2018
Exercises
Report the firstname, lastname and birthday of the members who has the same birthday as someone in Virginia
Is the following query correct?
SELECT lastname, firstname, region, birthday
FROM Members
WHERE birthday = ALL (SELECT birthday
FROM Members
WHERE region = 'GA' )
No! We cannot compare a single value with a LIST of values
4. Subqueries and joins CS122_W2014

14. Exercises (cont.) How about this query?
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Exercises (cont.)
How about this query?
SELECT lastname, firstname, region, birthday
FROM Members
WHERE birthday = (SELECT birthday
FROM Members
WHERE region = 'GA')
No! We cannot compare a single value with a LIST of values
We cannot compre 3 with (3,4,5,6)
4. Subqueries and joins CS122_W2014

15. Exercises (cont.) This one?
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Exercises (cont.)
This one?
SELECT lastname, firstname, region, birthday
FROM Members
WHERE birthday = ANY (SELECT birthday
FROM Members
WHERE region = 'GA')
Correct! =ANY is equivalent to IN
4. Subqueries and joins CS122_W2014

16. Joins
When SQL joins two tables you can select any column from either table as if they were both in same table
Joins tables "side-by-side"
Tables must share a common field
Primary Key – Foreign Key
Table 1
Table 2
4. Subqueries and joins CS122_W2014

17. How SQL Joins Tables Step 1: Create Cartesian Product
All possible combinations of data in both tables

18. How SQL Joins Tables Step 2: Eliminate Non-Matching Records

19. Join (another example)
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Join (another example)
When information is spread over multiple tables
Find the projects which John is working on
Projects
Employees
eid
pid 01 T4 X3 02 S2
eid
ename 01
John 02
Susan
4. Subqueries and joins CS122_W2014

20. Results eid ename pid John 01 T4 John 01 X3 02 S2 Susan pid T4 X3
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Results
eid
ename
pid
John 01 T4
John 01 X3 02 S2
Susan
pid T4 X3
4. Subqueries and joins CS122_W2014

21. The kinds of join Cross join Equi Join Inner join Outer join Self join
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The kinds of join
Cross join
Equi Join
Inner join
Outer join
Left join
Right join
Self join
4. Subqueries and joins CS122_W2014

22. Step1: Cartesian product
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Step1: Cartesian product
Join every row in the first table to every row in the second table
in every possible combination
Employees
Projects
eid
ename
pid
John 01 T4
John 01 X3
John 01 02 S2 01 T4
Susan 02 01 X3
Susan 02 02 S2
Susan
4. Subqueries and joins CS122_W2014

23. Step2: Throw out non-matching records
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Step2: Throw out non-matching records
pid
eid
ename
John 01 X3 T4 02 S2
Susan
Non-matching records
4. Subqueries and joins CS122_W2014

24. Cross Join
Builds a Cartesian product
Uses no ON keyword

25. Cross Join SELECT firstname, lastname, genre
| firstname | lastname | genre |
| Bob | Bentley | alternative |
| Lisa | Williams | alternative |
| Clint | Sanchez | alternative |
| Scott | Bull | alternative |
| Bob | Bentley | classical |
| Lisa | Williams | classical |
| Clint | Sanchez | classical |
| Scott | Bull | classical |
| Bob | Bentley | jazz |
| Lisa | Williams | jazz |
| Clint | Sanchez | jazz |
| Scott | Bull | jazz |
| Bob | Bentley | metal |
| Lisa | Williams | metal |
| Clint | Sanchez | metal |
| Scott | Bull | metal |
| Bob | Bentley | R&B |
| Lisa | Williams | R&B |
| Clint | Sanchez | R&B |
| Scott | Bull | R&B |
| Bob | Bentley | rap |
| Lisa | Williams | rap |
| Clint | Sanchez | rap |
| Scott | Bull | rap |
| Bob | Bentley | pop |
| Lisa | Williams | pop |
| Clint | Sanchez | pop |
| Scott | Bull | pop |
SELECT firstname, lastname, genre
FROM SalesPeople cross join Genre;
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26. Tips to join tables Find which tables to join: TA, TB
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Tips to join tables
Find which tables to join: TA, TB
Find the common attributes of those tables: field
Specify the relationship in the where clause: TA.field=TB.field
Put the two tables’ fields in the select clause as needed
4. Subqueries and joins CS122_W2014

27. Which fields to match (throw non-matching fields
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Equi Join example 1
List the CD title and the title of all tracks recorded in Studio 2
SELECT title, tracktitle
FROM Titles, Tracks
WHERE Titles.titleID = Tracks.titleID
AND studioID=2
Which tables to join
Which fields to match (throw non-matching fields
4. Subqueries and joins CS122_W2014

28. Equi Join example 2
List the names of members from Georgia (GA) and their salespeople. Select Members.Lastname, Members.FirstName, Salespeople.Lastname,Salespeople.Firstname
From Members, Salespeople
Where Members.SalesID= SalesPeople.SalesID And Region='GA'
4. Subqueries and joins CS122_W2014

29. Table Aliases Saves typing Table name cannot be used in rest of query
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Table Aliases
Saves typing
Table name cannot be used in rest of query
Case-sensitive in some systems
Example
List the names of members from Georgia (GA) and their salespeople
SELECT M.Lastname, M.FirstName, S.Lastname,S.Firstname
FROM Members M, Salespeople S
WHERE M.SalesID= S.SalesID And Region='GA'
4. Subqueries and joins CS122_W2014

30. 7/29/2018
Equi join example 3
List the names of all artists who have recorded a title and the number of titles they have
SELECT artistname, COUNT(Titles.artistID) AS
NumTitles
FROM Artists, Titles
WHERE Artists.artistID=Titles.artistID
GROUP BY artistname
4. Subqueries and joins CS122_W2014

31. Equi Join example 4 List the names of members in The Bullets.
Select Members.Lastname, Members.FirstName
From Members, XRefArtistsMembers, Artists
Where Members.MemberID = XRefArtistsMembers.MemberID
And Artists.ArtistID = XRefArtistsMembers.ArtistID
And Artistname = 'The Bullets'
4. Subqueries and joins CS122_W2014

32. Equi join summary The tables to join are in the FROM clause
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Equi join summary
The tables to join are in the FROM clause
Only join just enough tables
The relationship specifications are in the WHERE clause
WHERE clause will get messy if more tables are added
4. Subqueries and joins CS122_W2014

33. Inner Join Same result as Equi Join Different Syntax
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Inner Join
Same result as Equi Join
Different Syntax
Tables are listed with the keyword INNER JOIN
Relationship specifications moved from WHERE clause to ON clause
Free WHERE clause for traditional conditions
4. Subqueries and joins CS122_W2014

34. 7/29/2018
Inner Join example 1
List the CD title and the title of all tracks recorded in Studio 2
SELECT title, tracktitle
FROM Titles INNER JOIN Tracks
ON Titles.titleid = Tracks.titleid
WHERE studioID=2
Tables to join
Relationship
specification
4. Subqueries and joins CS122_W2014

35. Inner Join example 2
List the names of members from Georgia (GA) and their salespeople.
Select Members.Lastname, Members.FirstName, Salespeople.Lastname,Salespeople.Firstname
From Members Inner Join Salespeople
On Members.SalesID= Salespeople.SalesID
Where Region='GA'
4. Subqueries and joins CS122_W2014

36. 7/29/2018
Inner Join example 3
List the names of all artists who have recorded a title and the number of titles they have
SELECT artistname, COUNT(Titles.artistID)
AS NumTitles
FROM Artists INNER JOIN Titles
ON Artists.artistID=Titles.artistID
GROUP BY artistName
4. Subqueries and joins CS122_W2014

37. Inner Join example 4 List the names of members in The Bullets.
Select Members.Lastname, Members.FirstName
From Members Inner Join XrefArtistsMembers
On Members.MemberID = XRefArtistsMembers.MemberID
Inner Join Artists
On Artists.ArtistID = XRefArtistsMembers.ArtistID
Where Artistname = 'The Bullets'
Note: some systems require joins be grouped with parentheses.
List the names of members in The Bullets.
Select Members.Lastname, Members.FirstName
From (Members Inner Join XrefArtistsMembers
On Members.MemberID = XRefArtistsMembers.MemberID)
Inner Join Artists
On Artists.ArtistID = XRefArtistsMembers.ArtistID
Where Artistname = 'The Bullets'
4. Subqueries and joins CS122_W2014

38. Inner Join example 4 with Aliases
List the names of members in The Bullets.
Select M.Lastname, M.FirstName
From (Members M Inner Join XrefArtistsMembers X
On M.MemberID = X.MemberID)
Inner Join Artists A On A.ArtistID = X.ArtistID
Where Artistname = 'The Bullets'
4. Subqueries and joins CS122_W2014

39. Outer Join Left join Right join The order of tables MATTERS
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Outer Join
Left join
Report all of the records of the first (left) of two tables plus matching records in the second (right) table.
Right join
Report all of the records of the second (right) of two tables plus matching records in the first (left) table
The order of tables MATTERS
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40. Inner Joins vs. Outer Joins
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Inner Joins vs. Outer Joins
List the names of all artists who have recorded a title and the titles they have
SELECT Artistname, Title
FROM Artists A Inner Join Titles T
ON A.ArtistID=T.ArtistID
Artistname Title
The Neurotics Meet the Neurotics
Confused Smell the Glove
The Bullets Time Flies
The Neurotics Neurotic Sequel
Sonata Sonatas
Louis Holiday Louis at the Keys
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41. Inner Joins vs. Outer Joins
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Inner Joins vs. Outer Joins
List the names of all artists and the titles(if any) that they have recorded
SELECT Artistname, Title
From Artists A Left Join Titles T
ON A.ArtistID=T.ArtistID
Artistname Title
The Neurotics Meet the Neurotics
The Neurotics Neurotic Sequel
Louis Holiday Louis at the Keys
Word NULL
Sonata Sonatas
The Bullets Time Flies
Jose MacArthur NULL
Confused Smell the Glove
The Kicks NULL
Today NULL
21 West Elm NULL
Highlander NULL
5. More joins CS122_W2014

42. Another outer Join example
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Another outer Join example
List every genre from the Genre table and a count of the number of recorded tracks in that genre, if any
SELECT G.Genre, Count(Tracknum) As NumTracks
FROM (Genre G LEFT JOIN Titles TI
ON G.Genre = TI.Genre)
LEFT JOIN Tracks TR
ON TI.TitleID = TR.TitleID
GROUP BY G.Genre
5. More joins CS122_W2014

43. Using Outer Join to Duplicate NOT IN Functionality
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Using Outer Join to Duplicate NOT IN Functionality
Report artists who don’t have titles
SELECT A.ArtistID, Artistname, T.ArtistID
FROM Artists A Left Join Titles T
ON A.ArtistID=T.ArtistID
ArtistID Artistname ArtistID
The Neurotics
Louis Holiday
Word NULL
Sonata
The Bullets
Jose MacArthur NULL
Confused
The Kicks NULL
Today NULL
West Elm NULL
Highlander NULL
5. More joins CS122_W2014

44. Using Outer Join to Duplicate Not IN Functionality (cont.)
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Using Outer Join to Duplicate Not IN Functionality (cont.)
Report artists who don’t have titles
SELECT Artistname
FROM Artists A
Left Join Titles T
ON A.ArtistID=T.ArtistID
WHERE T.ArtistID Is Null
Artistname
Word
Jose MacArthur
The Kicks
Today
21 West Elm
Highlander
SELECT Artistname
FROM Artists
WHERE ArtistID NOT IN
(SELECT ArtistID FROM Titles)
Artistname
Word
Jose MacArthur
The Kicks
Today
21 West Elm
Highlander
5. More joins CS122_W2014

45. Joining on More Than One Column
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Joining on More Than One Column
Include AND in ON or WHERE clause to link on second, third, etc. columns
Works with either Equi Join or Inner/Outer Join syntax
Inner Join
Select TrackTitle
From Tracks T Inner Join AudioFiles A
On T.TitleID=A.TitleID And T.Tracknum=A.Tracknum
Where AudioFormat='MP3'
Equi Join
Select TrackTitle
From Tracks T, AudioFiles A
Where T.TitleID=A.TitleID And T.Tracknum=A.Tracknum
And AudioFormat='MP3'
5. More joins CS122_W2014

46. Self Joins Table 2 Table 2 Table 1 Joining two tables Self Join
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Self Joins
Joining two tables
Self
Join
Table 2
Table 2
Table 1
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47. Example Self Joining Table
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Example Self Joining Table
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48. Self-Join Join a table to itself Can be either an INNER or OUTER JOIN
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Self-Join
Join a table to itself
Can be either an INNER or OUTER JOIN
A self join always uses two fields in a table.
Need to use table aliases for differentiate two instances of the same table
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49. Self Join Example
List the names of all salespeople who have supervisors along with the names of their supervisors.
Select Sales.Firstname As EmpFirst, Sales.Lastname as EmpLast,
Sup.Firstname as SupFirst, Sup.Lastname as SupLast
From Salespeople Sales Inner Join Salespeople Sup
On Sales.Supervisor=Sup.SalesID
EmpFirst EmpLast SupFirst SupLast
Bob Bentley Scott Bull
Lisa Williams Scott Bull
Clint Sanchez Bob Bentley

50. Joins Compared Inner (Equi) Joins Outer Joins Self Joins Cross Joins
Reports only matched rows
Outer Joins
Reports all of records from one table plus matching records from the other table
Self Joins
Column in one table matched to another column in same table
Cross Joins
Cartesian product without dealing with matches