DB Review Session

ER Diagrams 1

Where does the salary attribute belong?

Actorid

name

address

birthday

Acted In Movie

title

type

year

salary

id

name

Actor Acted In Movie

The entities in a relationship set identify the relationship

role

title

ER Diagrams 2

id

name

Actor Acted In Movie

The entities in a relationship set identify the relationship

How would we store information about a person who acted in one movie in several roles?

titleRole

title

ER Diagrams 2

ER Diagrams 3

Personid

name

age

FatherOf

Where would you put the arrow?

father

child

ER Diagrams 3

Personid

name

age

FatherOf

father

child

ER Diagrams 4

Directorid

name

produced Movie title

Actorid name

What does this mean?

A movie has at most one actor and one director

What does this diagram mean?

Directorid

name

Directed Movie title

A movie has exactly one director.

A director directs at least one movie.

ER Diagrams 5

Copy

copy number condition

Copy Of

Borrowed

Person

id

Booktitle

author

isbnOwned By

Libraryname

ER Diagrams 6

snopno

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Division 1

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Division 1

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Division 2

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Division 2

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Division 3

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Division 3

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SQL Aggregation 1

SELECT B.bid, COUNT(*)

FROM Boats B, Reserves R

WHERE R.bid=B.bid and B.color=‘red’

GROUP BY B.bid

What does this query return?

Tuples:

(id of a reserved red boat, # of reservations of the red boat)

SELECT B.bid, COUNT(*)

FROM Boats B, Reserves R

WHERE R.bid=B.bid

GROUP BY B.bid, B.color

HAVING B.color=‘red’

SQL Aggregation 2

What if we put the condition into the HAVING clause?

We have also to put the color in the grouping list!

Aggregation 3

SELECT color

FROM Boats B

GROUP BY color

HAVING max(count(bid))

What is wrong with this?

How would you fix it?

The Color for which there are the most boats

SELECT color

FROM Boats B

GROUP BY color

HAVING count(bid) >= ALL

(SELECT count(bid)

FROM Boats

GROUP BY Color)

SQL Aggregation 3

The Color for which there are the most boats

Compute Closure(X, F)

C := X

while there is a V W in F such that (V C)and (W C) do

C := C Wreturn C

Attribute Closure 1

R=ABCDE F={ABC, CEB, DA, BCE}

Attribute Closure 2

{A}+ =

{A,B}+ =

{B,D}+ =

{A}

{A,B,C,E}

{A,B,C,D,E}

IsDependencyPreserving(F,R1…k)for each X->Y in F do

if not IsPreserved(X,Y,R1…k)return false

return true

Dependency Preservation 1a

/* check if X->Y is preserved */IsPreserved(X,Y,R1…k)Z:=Xwhile changes to Z occur do for i=1 to k do Z:= Z ((Z Ri)+ Ri) if YZ return trueelse return false

Dependency Preservation 1b

Is the following decomposition dependency preserving?

R = ABCDE F = {A -> ABCDE, BC -> A, DE -> C} R1 = ABDE, R2 = DEC

Dependency Preservation 2

No! BC->A is not preserved

R = ABC. For each F below, decide whether R is in BCNF/3NF:

Normal Forms

F = {} F = {A -> B} F = {A -> B, A -> C} F = {A -> B, B -> C} F = {A -> B, BC -> A}