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Databases > Compsci Is For Nerds > Flashcards

Compsci Is For Nerds Flashcards

1
Q

Database

A

Collection of interrelated persistent data stores without unnecessary redundancies to serve one or more applications

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2
Q

DBMS

A

Database Management System enables users to create maintain and control access

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3
Q

DBMS Disadvantage

A

Complexity, cost of management, performance, converting old data

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4
Q

Rows and columns

A

Rows called records column given distinct nane

Must be unique to prevent redundancies

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5
Q

Field

A

Attribute within a record carrying data, makes primary key

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6
Q

Entity

A

A table, attributes are shown as column headings
Must have primary key
Things that can only have one instance cannot be entities

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7
Q

Candidate Key

A

Minimal number of attributes uniquely identifting occurence of an entity
Primary key is chosen candidate key to identify records

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8
Q

Attribute lore

A

If max amount of values is known it can be an attribute, if an attribute has its own attribute it should be a seperate entity referenced by ID

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9
Q

Weak entity vs Strong entity

A

Weak entity is a child as one box and strong entity is a parent as box with outline

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10
Q

1NF Check

A

A table must not have more than one entry in any field

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11
Q

1NF Fix

A

Duplicate the rest of the row in the offending field

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12
Q

Non 1NF problems

A

Slow search
Inserting deleting updating difficult and error prone
Wasted space

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13
Q

Key Field (Candidate Key)

A

Different for every row so can be used to identify each row

Fields may need to be combined to form a key

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14
Q

Dependent key

A

If we know the value of a record from other records it is dependent

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15
Q

B is dependent on A

A

A: Determinant
B: Dependent
Non key fields are dependent on key fields

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16
Q

2NF Check

A

Check in 1NF

All non key fields must depend on whole table key

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17
Q

2NF Fix

A

Two or more tables created to replace original table

18
Q

Non 2NF Problems

A

Information is duplicated
Null values may be required
Insertion, updating, deletion problematic

19
Q

3NF Check

A

Check in 2NF
All non key fields dependent on only the key
No transitive dependency

20
Q

3NF Fix

A

Two or more tables must be created to replace original table

21
Q

3NF Inconsistency

A

If more than one possible candidate key, which is composite and the keys share a common field

22
Q

BCNF Check

A

Check in 3NF

Check all determinants in a relation must be candidate keys

23
Q

BCNF Fix

A

The fields that depend on the field which is not a candidate key must be removed and put into a new table with their determinants as key

24
Q

What do fourth and fifth normal forms deal with

A

3 or more key fields and no dependent fields

25
Q

4NF Check

A

Check in BCNF

No independent multi-value dependencies

26
Q

4NF Fix

A

Split the table so there is no more than one MVD in each of the new tables
3 way multi dependency into 2 two way dependencies

27
Q

5NF Check

A

Check in BCNF

Check table without any related multi-valued dependencies

28
Q

Related Multi Value Dependencies

A

MVD not totally independent of each other

Not all possible combinations occur in the data

29
Q

5NF Fix

A

Split table into 3 tables so that there is no more than one MVD in each of the new tables
3 way multiple dependency broken down to 3 2 way dependencies

30
Q

DBMS Needs

A

DDL - Data Definition Language

DML - Data Manipulation Language

31
Q

DDL

A

User can create new objects with create alter and drop statements

32
Q

DDL Syntax

A

Create Table table-name (column-details)
Drop Table table-name
Alter Table table-name command column-details

33
Q

Column details

A

Record name with data type

E.g ID_Num INTEGER,…

34
Q

Column types

A

Char, Varchar, Integer, Numeric, Boolean, Date

35
Q

Type info

A

Char is fixed while varchar is variable

Numeric(n,m) where n and m are digits after decimal

36
Q

Data Manipulation Language

A

User can retrieve, insert, delete and update data in a database

37
Q

DML Insert

A

Insert Into table-name (columns)
Values (value-list)
Can name columns where any unmentioned columns are set to null
Can copy data using select

38
Q

DML Update

A

Update table-name
Set column-assignments
Where conditions

39
Q

Column assisgnments

A

List of assignments separated by commas of form:

column-name = new-value

40
Q

DML Delete

A

Delete From table-name

Where conditions

41
Q

View Syntax

A

Create View view-name As
Select (x) from emp/dept etc.

Can make view based on another view

42
Q

Why create a view

A

Restrict access
Save complex expressions
Sort/group information
Make Logical Data Independence

Databases (2 decks)

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