1. CS122 Using Relational Databases and SQL
10/29/2019
CS122 Using Relational Databases and SQL
4. Subqueries and joins
Daniel Firpo
Slides prepared by Randy Moss
Department of Computer Science
California State University, Los Angeles

2. Outline Subqueries Joining tables Subqueries in the WHERE clause
10/29/2019
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 CS1222-S2019

3. Sub-Queries A query within a query Sub-query placed in parentheses
10/29/2019
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 CS1222-S2019

4. Sub-Queries examples (1)
10/29/2019
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 CS1222-S2019

5. Sub-Queries examples (1)
10/29/2019
Sub-Queries examples (1)
Combine the two queries
SELECT firstname, lastname
FROM Members
WHERE birthday = (SELECT Min(birthday)
FROM Members )
4. Subqueries and joins CS1222-S2019

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)
10/29/2019
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 CS1222-S2019

8. Sub-Queries examples (2)
10/29/2019
Sub-Queries examples (2)
Combine the two queries
SELECT tracktitle, lengthseconds
FROM Tracks
WHERE lengthseconds > ( SELECT Avg(lengthseconds) FROM Tracks )
4. Subqueries and joins CS1222-S2019

9. 10/29/2019
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 CS1222-S2019

10. ALL & ANY Used with Sub-Queries
10/29/2019
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 CS1222-S2019

11. ALL example
10/29/2019
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 CS1222-S2019

12. ANY example WHERE region = 'GA' )
10/29/2019
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 CS1222-S2019

13. 10/29/2019
Exercises
Report the firstname, lastname and birthday of the members who has the same birthday as someone in Georgia
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 CS1222-S2019

14. Exercises (cont.) How about this query?
10/29/2019
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 CS1222-S2019

15. Exercises (cont.) This one?
10/29/2019
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 CS1222-S2019