Relational Algebra

Question 1

What is relational algebra

Answer 1

It defines the theoretical ways of manipulating table contents using relational operators.

Question 2

what are the relational operatros

Answer 2

• Union / Intersect
• Difference / Product
• Select / Project / Join / Divide

Question 3

Unary operator

Answer 3

work on one table at a time.

Question 4

Select

Answer 4

yields values for all rows in a table satisfying a certain condition.

Question 5

project

Answer 5

yields values for selected attributes. (cols).

Question 6

Union

Answer 6

combines rows from two tables excluding duplicates.

Question 7

what is union-compatible

Answer 7

the two tables must have the same attribute characteristics.

Question 8

Intersect

Answer 8

yields the rows that appear in both tables.

must be union- compatible.

Question 9

Difference

Answer 9

Yield all rows that are in the first table that are not found in the second table.

Question 10

product

Answer 10

AKA catersian product

• yields all possible pairs of rows from two tables.

Question 11

What is a join

Answer 11

A join allows information to be intelligently combined from two or more tables.

Question 12

Natural join or Inner join

Answer 12

Returns the matched records from the tables being joined.

Naturally by:
-product
-select
-project

Question 13

Outer join

Answer 13

The matched pairs would be retained, and any unmatched values in the
other table would be left null.

Question 14

Left Outer join

Answer 14

All the matched rows as well as the unmatched rows of the left table. RIght will be null.

Question 15

Right outer join

Answer 15

All matched rows plus the unmatched rows of the right table. left will be null.

Question 16

Divide

Answer 16

identifying rows from one table associated with all rows in another.

Question 17

Data dictionary

Answer 17

A detailed description of all tables in the database.

Contains the attribute names and characteristics of the table as well as metadata.

Question 18

System catalog

Answer 18

Same as a Data dick.

Question 19

Explain the bridge bitch

Answer 19

M:N not supported directly in relational environment.

bridge entity added between to make it 1:M and M:1…. you know this

Question 20

what are Indexes

Answer 20

An index is an orderly arrangement used to logically access rows in a table.

• spoeds the data retrieval.

Question 21

structure of an index

Answer 21

• Has a index key and a set of pointers.

Index key is the reference point.
The pointers point to the location of the data.