Summary
Summary Databases (INFODB)
- Course
- Institution
All the subjects discussed in the Databases course, clearly summarized in a structured way. Based on the lectures, recorded clips and the book Database Systems - The Complete Book.
[Show more]
Seller
Follow
Suniht
Reviews received
Content preview
DatabasesRelational algebra 1
ERD 3
Normalisation 4
SQL 7
Indexing 10
Transaction processing 11
Concurrency 11
Recovery 13
Two-Phase-Commitment Protocol 16
Query processing 19
EXtended RA 19
Access strategy 20
,Relational algebra
Super key A set of attributes that uniquely defines every tuple of the table
Candidate key A minimal super key; Super key of which no proper subset exists that itself is
also a super key
Primary key A specific candidate key, usually one attribute in the form of a number
Foreign key Reference to the primary key of one table in another table
Unary operators
- σ, selection: reduces the number of tuples in the table
- π, projection: reduces the number of attributes in the table
- composition: combines multiple operations
- :=, assignment: assigns an expression (a table) to a name T ( T := <expr> )
- renaming attributes: also renames attributes ( T[A1, … , An] := <expr> )
- ρ, rename: renames the expression to a name T ( ρ(T)(<expr>) )
- Also rename attributes: ρ(T, A1, … , An)(<expr>)
Binary operators
- ∪, union: combines two tables (duplicates are eliminated)
- -, difference: deletes elements from the left operand that also occur in the right operand
- ∩, intersection: retains only the elements that occur in both operands
- ×, cartesian product: all possible combinations of tuples from both operands
- Number of combinations is number of tuples on the left × number of tuples right
R S R×S
A B C D A B C D
a 11 b 25 → a 11 b 25
b 43 c 41 a 11 c 41
b 43 b 25
b 43 c 41
- ⨝θ, theta-join: all possible combinations of tuples under condition theta (θ)
R S R ⨝θ S
A B C D A B C D
a 11 b 55 → b 43 b 21
b 43 c 31 c 37 c 31
c 37 b 21
θ : (R.A = S.C) ∧ (R.B > S.D)
1
, - ⨝, natural join: all possible combinations of tuples that form a match on some attribute
- Order of operands doesn’t matter
- If there are no matching attributes, natural join is equivalent to cartesian product
R S R⨝S
A B A D A B D
a 11 b 55 → b 43 55
b 43 c 31 b 43 21
c 37 b 21 c 37 31
d 17
- ÷, division: all values under attribute A that are associated with at least the values from
the other operand under attribute B
R S R÷S
A B B A
1 1 1 → 1
1 3 3 8
2 2
2 3
8 1
8 3
8 7
Examples
- Names of the readers who loaned at least one Dickens book:
πname(Reader ⨝ Loan ⨝ (σauthor = “Dickens” Book))
- Names of the readers who have never loaned a Dickens:
πname(Reader) - πname(Reader ⨝ Loan ⨝ (σauthor = “Dickens” Book))
- Names of the readers who have loaned only Dickens books:
πname(Reader) - πname(Reader ⨝ Loan ⨝ (σauthor != “Dickens” Book))
- Names of the readers who have loaned all Dickens books:
πname(Reader ⨝ (πrid, bid(Loan) ÷ πbid(σauthor = “Dickens” Book)))
- Assign a table to a variable with and without changing the attribute names:
OldMovies := πid, title(σyear < 1930 Movie)
OldMovies[omid, omtitle] := πid, title(σyear < 1930 Movie)
- Renaming a variable in-line:
… ⨝ ρ(OldMovies, omid, omtitle)(πid, title(σyear < 1930 Movie))
2
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card or Stuvia-credit for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller Suniht. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for $10.80. You're not tied to anything after your purchase.
Can Stuvia be trusted?
4.6 stars on Google & Trustpilot (+1000 reviews)
56326 documents were sold in the last 30 days
Founded in 2010, the go-to place to buy study notes for 14 years now