1. Database Management Systems
Faculty of Computer Science
Technion – Israel Institute of Technology
Database Management Systems
Course
Tutorial 4:
SQL Queries

2. Database example Library Database Ordered Cust_Id Book_Id Order_Date
Books
Book_Id
Book_Name
Year
Max_Time
Faculty
Pages
Customers
Cust_Id
Cust_Name
Faculty
Borrowed
Cust_Id
Book_Id
From_Date
To_Date

3. Database example Customers(Cust_Id, Cust_Name, Faculty)
Cust_Id: Customer ID (unique)
Cust_Name: Customer Name
Faculty: Faculty Name

4. Database example Customers(Cust_Id, Cust_Name, Faculty) FacultyCS
Moshe Cohen
12345 EE
Avi Barak
23456
MED
34567
Lior Edri
45678
56789
67890
Two Avi Barak, different faculties
Two Moishe Cohen in EE

5. Database example
Books(Book_Id, Book_Name, Year, Max_Time, Faculty, Pages)
Book_Id: Unique book id
Book_Name: Bool title
Year: Year of print
Max_Time: Maximum borrowing time in days
Faculty: Faculty name
Pages: Page number

6. Database And Knowledge
Database example
Books(Book_Id, Book_Name, Year, Max_Time, Faculty, Pages)
Faculty
Pages
Max_Time
Year
Book_Name
Book_Id CS
348 7
1998
Database Systems
1111 14
1112
424
2001
1113
390 1
Database And Knowledge
2222 EE
2223
180 21
Electronic Circuits
3333
MED
580
1985
Genes 7
4444
450
1988
Anatomy
5555

7. Database example Ordered(Cust_Id, Book_Id, Order_Date)
Cust_Id: Customer ID
Book_Id : Book ID
Order_Date: Date of book order

8. Database example Ordered(Cust_Id, Book_Id, Order_Date) Order_Date
14-Oct-2002
1111
12345
24-Oct-2002
1112
45678
30-Oct-2002
1113
12-Oct-2002
2222

9. Database example Borrowed(Book_Id, Cust_Id, From_Date, To_Date)
Book_Id: Book ID
Cust_Id: Customer ID
From_Date: Borrowing date
To_Date: Return date

10. Database example Borrowed(Book_Id, Cust_Id, From_Date, To_Date)
13-Oct-2002
56789
5555

11. Outline

12. SQL Queries: Sort
SELECT select_list FROM table_expression ORDER BY sort_expression1 [ASC | DESC] [NULLS { FIRST | LAST }] [, sort_expression2 [ASC | DESC] [NULLS { FIRST | LAST }] ...]

13. SQL Queries: Sort Return the costumers names and ids ordered by
customer name (in ascending order) and by
ids in descending order
SELECT cust_name, cust_id
FROM customers
ORDER BY cust_name, cust_id DESC

14. SQL Queries: Sort Customers(Cust_Id, Cust_Name, Faculty) FacultyCS
Moshe Cohen
12345 EE
Avi Barak
23456
MED
34567
Lior Edri
45678
56789
67890
Two Avi Barak, different faculties
Two Moishe Cohen in EE

15. SQL Queries: Sort
SELECT cust_name, cust_id FROM customers ORDER BY cust_name, cust_id DESC
Cust_Name
Cust_Id
Avi Barak
34567
23456
Lior Edri
45678
Moshe Cohen
67890
56789
12345

16. SQL Queries: LIMIT & OFFSET
SELECT select_list
FROM table_expression
[ ORDER BY ... ]
[ LIMIT { number | ALL } ] [ OFFSET number ]
Must use ORDER BY while using LIMIT/OFFSET
Allows to return a range of sorted result
The indices are determined by the ORDER BY

17. SQL Queries: LIMIT & OFFSET
Return the 3rd and 4th customers from previous query
SELECT cust_name, cust_id
FROM customers
ORDER BY cust_name, cust_id DESC

18. SQL Queries: LIMIT & OFFSET
cust_name
cust_id
Avi Barak
34567
23456
Lior Edri
45678
Moshe Cohen
67890
56789
12345
SELECT cust_name, cust_id
FROM customers
ORDER BY cust_name, cust_id DESC
OFFSET 2
LIMIT 2
cust_name
cust_id
Lior Edri
45678
Moshe Cohen
67890

19. SQL Queries: SET Operations
UNION
query1 UNION [ALL] query2
INTERSECT
query1 INTERSECT [ALL] query2
EXCEPT
query1 EXCEPT [ALL] query2
Keep duplicates

20. SQL Queries: SET Operations
Recall
A table is a bag of tuples
Not a set since the same tuple can appear several times
We can specify how to handle duplicates:
To keep them we write the operation name + ALL
To eliminate we just write the operation name
To perform set operations schemas must be type-equal

21. SQL Queries: SET Operations
Example: Return the customers id that preformed an action in the library (borrowed or ordered a book)
SELECT Cust_Id from orderd
UNION
SELECT Cust_Id from borrowed

22. SQL Queries: SET Operations
SELECT Cust_Id from orderd UNION SELECT Cust_Id from borrowed
Order_Date
Book_Id
Cust_Id
14-Oct-2002
1111
12345
24-Oct-2002
1112
45678
30-Oct-2002
1113
12-Oct-2002
2222
To_Date
From_Date
Cust_Id
Book_Id
13-Oct-2002
56789
5555

23. SQL Queries: SET Operations
SELECT Cust_Id from orderd UNION SELECT Cust_Id from borrowed
Cust_Id
12345
45678
cust_id
56789
12345
45678
Cust_Id
56789

24. SQL Queries: SET Operations
SELECT Cust_Id from orderd UNION SELECT book_id from borrowed
Cust_Id
12345
45678
cust_id
55555
12345
45678
Book_id
55555

25. SQL Queries: SET Operations
SELECT Cust_Id from orderd UNION SELECT from_date from borrowed Problem – date and ID are of different types

26. SQL Queries: WITH
WITH creates a temporary table to use within the query you write
Unlike views, this temporary table is calculated only as a part of the query, and its definition is not saved on the server.
WITH TempCSBooks as (
SELECT Book_Id, Book_Name
FROM Books
WHERE Faculty = 'CS' )
SELECT * FROM TempCSBooks

27. SQL Queries: WITH RECURSIVE
WITH RECURSIVE allows to preform calculations can not be done with standard SQL syntax
Calculations are done until reaches fixpoint
The current calculations does not change the result of the previuos one
Example: calculate the sum of all the numbers from 1 to 100
WITH RECURSIVE t(n) AS (
VALUES (1)
UNION
SELECT n+1 FROM t WHERE n < 100 )
SELECT sum(n) FROM t;
At each step the input is the ouput of the prev step

28. SQL Queries: WITH RECURSIVE
𝑟 0
𝑟 1
𝑟 2
𝑟 99 N 1 N 2 N 3 … N
100
𝑖 𝑟 𝑖
At each step the input is the ouput of the prev step N 1 2 ….
100

29. SQL Queries: WITH RECURSIVE
given a table of edges in the graph, find all paths without a cycle
For a non-fixpoint queries this cannot be done
We need to know how much JOIN operations to make
Source
Destination 1 2 3 4

30. SQL Queries: WITH RECURSIVE
Arrays:
Add element \ array concatenation : ||
[1,2,3] || 4 => ]1,2,3,4]
You can use the ANY \ ALL operator to check if a value is in array
4 =ANY [1,2,3,4]
More information:

31. SQL Queries: WITH RECURSIVE
WITH RECURSIVE find_paths(source, destination, length, path, cycle) AS ( SELECT source, destination, 1, ARRAY[source], false FROM edges e UNION ALL SELECT fp.source, e.destination, fp.length + 1, path || e.source, e.source = ANY(path) OR e.destination = ANY(path) FROM edges e, find_paths fp WHERE e.source = fp.destination AND NOT cycle ) SELECT * FROM find_paths WHERE NOT cycle order by source, destination, length;

32. SQL Queries: WITH RECURSIVE
source
destination
length
path
cycle 1 2
[1]
FALSE
[1, 3] 3
[1, 3, 4]
[1, 2] 4
[1, 3, 2]
[1, 2, 3]
[2]
[2, 3]
[3]
[3, 4]
[3, 2]
[4]
[4, 2]