Week 4

Question 1

What is the Relational algebra

Answer 1

A mathematical query language that forms the basis of the SQL query language

Question 2

What is the Selection operation do?

Answer 2

Selects a subset of rows from relation.

Question 3

What is the Projection operation do?

Answer 3

Deletes unwanted columns from relation.

Question 4

What is the Cross-product operation do

Answer 4

Combines two relations.

Question 5

What is Set-difference operation do?

Answer 5

Tuples in relation 1, but not in relation 2.

Question 6

What is the Union operation do?

Answer 6

Tuples in relation 1 and relation 2

Question 7

What will the Schema of the result contain after the projection?

Answer 7

Projection operator eliminate duplicates.

Question 8

What will the Schema of the result contain after the selection?

Answer 8

The selection operator, selects rows that satisfy selection condition

Question 9

What will the Schema of result be after the relational algebra operation?

Answer 9

Result relation can be the input for another relational algebra operation

Question 10

Union Example

Answer 10

Question 11

Intersection Example

Answer 11

Question 12

Set difference example

Answer 12

Question 13

Cross Product example

Answer 13

Question 14

Both S1 and R1 have a field called sid, Which may cause a conflict when referring to columns

Answer 14

Rename an operator by taking a relation schema and gives a new name to the schema and the columns

Question 15

What would this Condition join statement equivalent to

Answer 15

Question 16

What is an Equi-Join

Answer 16

A special case of condition join where the condition c contains only equalities

Question 17

What would the statement A / B means where A have 2 fields, x and y; B has only the field y.

Answer 17

A/B contains all x values (players) such that for every y value (game) in B, there is an x-y paired value in A

Question 18

Find names of sailors who’ve reserved boat #103

Answer 18

Question 19

Find names of sailors who’ve reserved a red boat

Answer 19

Question 20

What is the 4 conceptual evaluation strategies?

Answer 20

1. Comput the cross-product of relation-list.
2. Discard resulting tuples if they do not satisfy the conditions.
3. Display attributes that are in attribute-list.
4. If DISTINCT is specified, eliminate duplicate rows.

Question 21

Why do we do decomposition?

Answer 21

Are done to remove redundant data that can lead to anomalies

Question 22

What is the 1st normal form says?

Answer 22

specifies that all tables in a relational database must be structured so that each column contains atomic values. In other words, each column of a table must hold only a single, indivisible value.

Question 23

What is the 2nd normal form says?

Answer 23

Specifies that a table must be in 1NF and should not have any partial dependencies. In other words, each non-key column in a table should be dependent on the entire primary key, not just part of it.

Question 24

What is the 3rd normal form says?

Answer 24

Specifies that a table must be in 2NF and no non-prime attribute determines a non-prime attribute (only keys can determine!).