1. Basic SQL Queries Go over example queries, like 10 > ALL.
Show how create assertion fails.
Check into setting up queries in SQL Server.

2. Introduction
Introduce SQL, the standard query language for relational DBS.
An SQL query takes one or more input tables and returns one output table.
We’ll start with the case of one input table

3. Example Instances bid colour 101 green 103 red Sailors Boats Reserves
cmpt354.c4_sailors1
Reserves

4. Overview Basic SQL syntax Set Operations Joins Advanced Queries
nested queries
comparing sets, strings.

5. Sinlge-Table SQL Queries

6. Basic SQL Syntax table A table name (possibly with a range-variable).
SELECT [DISTINCT] target-list
FROM table
WHERE qualification
table A table name (possibly with a range-variable).
target-list A list of attributes of relations in relation-list
qualification Comparisons (Attr op const or Attr1 op Attr2, where op is one of ) combined using AND, OR and NOT.
DISTINCT is an optional keyword indicating that the answer should not contain duplicates. Default is that duplicates are not eliminated!
Implementation in SQL different from relational model – multiset vs. set.
“select” in SQL = “project” in Relational Algebra.

7. Conceptual Evaluation
Semantics of an SQL query defined in terms of the following conceptual evaluation strategy:
Retrieve the tuples in table.
Discard resulting tuples if they fail qualifications.
Delete attributes that are not in target-list.
If DISTINCT is specified, eliminate duplicate rows.

8. Basic Operators in SQL

9. SELECT (columns, values)
SELECT S.sname
FROM Sailors S
Write out relational algebra, as exercise

10. WHERE The WHERE clause selects/filters rows. SELECT * FROM Sailors S
WHERE S.sid = 58

11. Renaming Relations: Views
A view is just a relation, but we store a definition, rather than a set of tuples.
Any SQL query can be stored as a view.
Views can be dropped using the DROP VIEW command.
CREATE VIEW
MySailors (sid, name)
AS SELECT S.sid, S.sname
FROM Sailors S
WHERE S.age = 45.0 OR S.rating = 10
Set up and Illustrate in SQL Server. Do views later?
How to handle DROP TABLE if there’s a view on the table?
DROP TABLE command has options to let the user specify this.
Contrast with rho notation ion relational algebra. 18

12. Renaming Columns the AS keyword can be used to rename columns.
SELECT S.sid AS SailorSid, R.sid AS ReserveSid
FROM Sailors S, Reserves R
Set up and Illustrate in SQL Server. Do views later?
How to handle DROP TABLE if there’s a view on the table?
DROP TABLE command has options to let the user specify this.
Contrast with rho notation ion relational algebra. 18

13. Expressions and Strings
SELECT S.age, age1=S.age-5, 2*S.age AS age2
FROM Sailors S
WHERE S.sname LIKE ‘b_%b’
Illustrates use of arithmetic expressions and string pattern matching: Find results for sailors whose names begin and end with B and contain at least three characters.
AS and = are two ways to name fields in result.
LIKE is used for string matching. `_’ stands for any one character and `%’ stands for 0 or more arbitrary characters. case sensitivity Oracle on Strings
By default, like is case insensitive. Can make it case sensitive, it’s a bit complicated funny
See also Oracle solution
For character length: SELECT titles.*, LEN(title) AS TitleLength FROM titles

14. Basic SET Operators iN SQL

15. Union Find sid’s of sailors who are 45 years old or have rating 10.
UNION: Can be used to compute the union of any two union-compatible sets of tuples (which are themselves the result of SQL queries).
If we replace OR by AND in the first version, what do we get?
SELECT S.sid
FROM Sailors S
WHERE S.age = 45.0 OR S.rating = 10
SELECT S.sid
FROM Sailors S
WHERE S.age = 45.0
UNION
WHERE S.rating = 10
Answer1: boats that are both red and green.
% Answer 2: sailors with red boats – sailors with green boats.

16. Intersections
Find sid’s of sailors who are 45 years old and have rating 10.
INTERSECT: Can be used to compute the intersection of any two union-compatible sets of tuples.
Not supported in Mysql, but yes in SQL Server
SELECT S.sid
FROM Sailors S
WHERE S.age = 45.0
INTERSECT
WHERE S.rating = 10

17. Set Difference
Find sid’s of sailors who are 45 years old and do not have rating 10.
EXCEPT: Can be used to compute the set difference of any two union-compatible sets of tuples.
Not supported in MySQL but yes in SQL Server.
SELECT S.sid
FROM Sailors S
WHERE S.age = 45.0
EXCEPT
WHERE S.rating = 10
What does this query return?

18. multiple tables
Table Joins

19. Basic SQL Syntax
SELECT [DISTINCT] target-list
FROM relation-list
WHERE qualification
relation-list A list of table names (possibly with range-variables).
target-list A list of attributes of relations in relation-list
qualification Comparisons (Attr op const or Attr1 op Attr2, where op is one of ) combined using AND, OR and NOT.
Implementation in SQL different from relational model – multiset vs. set.
“select” in SQL = “project” in Relational Algebra.

20. Conceptual Evaluation
Semantics of an SQL query defined in terms of the following conceptual evaluation strategy:
Compute the cross-product of relation-list.
Discard resulting tuples if they fail qualifications.
Delete attributes that are not in target-list.
If DISTINCT is specified, eliminate duplicate rows.
Short version:
compute the cross-product of the named tables.
Apply single-table evaluation to cross-product.

21. Example of Conceptual Evaluation
SELECT *
FROM Sailors S, Reserves R
WHERE S.sid=R.sid AND R.bid=103
Try in SQL Server or mysql
First equality is join condition. Try leaving it out.

22. Cross Product FROM List is interpreted as cross product.
SELECT *
FROM Sailors, Reserves
With JOIN keyword
SELECT *
FROM Sailors CROSS JOIN Reserves

23. Joining Two Tables WHERE clause specifies selection condition SELECT *
FROM Sailors S, Reserves R
WHERE S.sid=R.sid
(sid)
sname
rating
age
bid
day 22
dustin 7
45.0
101
10/10/96 58
103
11/12/96 31
lubber 8
55.5
rusty 10
35.0
Try in SQL Server.
First equality is join condition. Try leaving it out.

24. JOIN ON With JOIN keyword ON replaces WHERE SELECT *
FROM Sailors S JOIN Reserves R
ON S.sid=R.sid AND R.bid=103
Check correctness

25. Natural Join forces equality on columns with the same name.
SELECT * FROM
Sailors NATURAL JOIN Reserves
forces equality on columns with the same name.
Not supported in SQL Server but yes in MySQL.
Can replace INTERSECT.
SELECT * FROM
(SELECT S.sid
FROM Sailors S
WHERE S.age = 45.0
NATURAL JOIN
SELECT S.sid
WHERE S.rating = 10)
CHECK QUERY.
Natural Join doesn’t work in SQL server, see . But it does work in MySQL.

26. MySQL Natural Join Syntax
SELECT * FROM
(SELECT S.sid
FROM Sailors S
WHERE S.age = 45.0) SailorAge
NATURAL JOIN
WHERE S.rating = 10) SailorRating;
view idea is important for assignment 2
must name derived (defined) tables
could use views instead

27. Examples and Exercises

28. Natural Join Exercise What is the natural join of a table with itself?
e.g. select * from Sailors natural join Sailors?
What is the natural join of two tables that have exactly the same columns?
Answer. 1: you get back the original table. Idempotence. 2. the intersection of the two tables.

29. Find sailors who’ve reserved at least one boat
SELECT S.sid
FROM Sailors S, Reserves R
WHERE S.sid=R.sid
Would adding DISTINCT to this query make a difference?
What is the effect of replacing S.sid by S.sname in the SELECT clause? Would adding DISTINCT to this variant of the query make a difference?
Answer 1: yes, if sailors can reserve more than one boat.
Answer 2: may lead to loss of information if sailors with different ids have the same name
“not equals” = <>. Or !=. See .
Try this out in SQL Server.

30. Exercise Write the following queries in SQL:
Find sid’s of sailors who have reserved a red or a green boat.
Find sid’s of sailors who have reserved a red and a green boat.
SELECT R.sid
FROM Boats B, Reserves R
WHERE R.bid=B.bid
AND B.color=‘red’
UNION
WHERE R.bid=B.bid
AND B.color=‘green’
For 2: SELECT R.sid
INTERSECT
Or using natural join:
select * from
(SELECT R.sid
AND B.color='red') RedBoatSailors
Natural join
AND B.color='green') GreenBoatSailors;

31. Operator Exercise
Consider the following schema.
Suppliers(sid: integer, sname: string, address: string)
Parts(pid: integer, pname: string, color: string)
Catalog(sid: integer, pid: integer, cost: real)
The Catalog lists the prices charged for parts by Suppliers. Write the following queries in SQL:
Find the pnames of parts for which there is some supplier.
Find the sids of suppliers who supply a red part or a green part.
Find the sids of suppliers who supply a red part and a green part.

32. Intermediate SQL
start with Canvas quiz

33. Set Membership
Find sailors who are 45 years old and have rating 10.
<tuple> IN <relation> returns TRUE if the tuple is contained in the relation.
Can replace INTERSECT.
SELECT *
FROM Sailors S
WHERE S.age = 45.0 AND
S.sid IN
(SELECT sid
FROM Sailors
WHERE rating = 10)

34. NOT IN can replace EXCEPT
Find sid’s of sailors who are 45 years old and do not have rating 10.
SELECT S.sid
FROM Sailors S
WHERE S.age = 45.0
AND
S.sid NOT IN
(SELECT sid
FROM Sailors
WHERE rating = 10)
Look up lack of support.
What does this query return?

35. Nested Queries

36. Nested Queries
SELECT S.sid
FROM Sailors S
WHERE
S.sid NOT IN
(SELECT sid
FROM Sailors
WHERE rating = 10)
A powerful feature of SQL: a WHERE clause can itself contain an SQL query!
So can FROM clauses.
To find sailors who’ve not reserved #103, use NOT IN.
To understand semantics of nested queries, think of a nested loops evaluation: For each Sailors tuple, check the qualification by computing the subquery.
Debugging hint: write and run subqueries first.

37. Nested Queries with Correlation
Find names of sailors who’ve reserved boat #103:
SELECT S.sname
FROM Sailors S
WHERE EXISTS (SELECT *
FROM Reserves R
WHERE R.bid=103 AND S.sid=R.sid)
EXISTS <query> returns TRUE if the query is not empty.
Subquery must be re-evaluated for each Sailors tuple.
Unique (instead of exists) checks for duplicates with respect to entire row. True iff no row appears twice.
Illustrates use of *. Without R.bid, we may have two reservations that don’t appear twice.
Unique doesn’t seem to have been implemented in SQL server (or anywhere) If UNIQUE is used, and * is replaced by R.bid, finds sailors with at most one reservation for boat #103. (UNIQUE checks for duplicate tuples; * denotes all attributes. Why do we have to replace * by R.bid?)

38. “All” Queries in SQL Find sailors who’ve reserved all boats.
SELECT S.sname
FROM Sailors S
WHERE
not EXISTS
((SELECT B.bid
FROM Boats B)
EXCEPT
(SELECT R.bid
FROM Reserves R
WHERE R.sid=S.sid))
The negation trick.
Find sailors who have not reserved all boats.
Use NOT or EXCEPT to find the others.
exists a not reserved boat?
find all boats
show venn diagram
show 1st-order logic
/* find boats that have been reserved by Sailor */
find boats that have been reserved by Sailor S

39. Exercise ctd.
Consider the following schema.
Suppliers(sid: integer, sname: string, address: string)
Parts(pid: integer, pname: string, color: string)
Catalog(sid: integer, pid: integer, cost: real)
The Catalog lists the prices charged for parts by Suppliers. Write the following queries in SQL. You can use NOT EXISTS.
Show examples of tuples that do and don’t satisfy the condition
1. SELECT S.sid
FROM Suppliers S
EXCEPT
/* a part that is supplied by sid and not red */
(SELECT C.sid
FROM Parts P, Catalog C
WHERE P.pid = C.pid
AND P.color <> ‘red’) 2.
SELECT S.sname
WHERE NOT EXISTS
/*find parts that have not been supplied by sid*/
((SELECT P.pid FROM Parts P)
/*find all parts supplied by sid */
(SELECT C.pid
FROM Catalog C
WHERE C.sid = S.sid))
Find the sids of suppliers who supply only red parts.
Find the snames of suppliers who supply every part.

40. Set comparisons

41. More Set-Comparison Operators
We’ve already seen IN, EXISTS.
Also available: op ANY, op ALL
Find sailors whose rating is greater than that of some sailor called Horatio:
SELECT *
FROM Sailors S
WHERE S.rating > ANY (SELECT S2.rating
FROM Sailors S2
WHERE S2.sname=‘Horatio’)
Any: there is some member of set that makes comparison true. False on empty set.
All: all members of set make comparison true. True on empty set.
Hacky!
Maybe go to Aggregation Functions now.

42. Simple Examples for Any and All
1 = Any {1,3} True
1 = All {1,3} False
1 = Any {} False
1 = All {} True

43. Exercise (III)
Consider the following schema.
Suppliers(sid: integer, sname: string, address: string)
Parts(pid: integer, pname: string, color: string)
Catalog(sid: integer, pid: integer, cost: real)
The Catalog lists the prices charged for parts by Suppliers. Write the following query in SQL using the ALL construct,
solution for the only red parts example using ALL
Select S.sid from Suppliers S
where ‘Red’ = ALL (select Parts.color
from Catalog, Parts
where Catalog.sid = S.sid and Parts.pid = Catalog.pid )
/* the inner query finds the colors of all parts supplied by the supplier. */
Find the snames of suppliers who supply only red parts.

44. Summary: SQL Set Operators
UNION, INTERSECT, EXCEPT behave like their set theory/relational algebra counterpart.
New Operator EXISTS tests if a relation is empty.
Can use ANY, ALL to compare a value against values in a set.