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exchanging data > Databases > Flashcards

Databases Flashcards

1
Q

What is a database

A

A structured, persistent store of data, organised so that it can be easily accessed, managed and updated

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2
Q

Describe a field

A
  • Stores a single piece of data
  • Has a specified data type
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3
Q

Define a record

A

A collection of fields composing an entry in a database

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4
Q

Define a table

A

A complete set of records

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5
Q

What do databases make it convenient to do

A
  • Access data
  • Update data
  • Search for data
  • Present data in a suitable way
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6
Q

Define flat-file databases

A

Databases in which all data is stored in a single table

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7
Q

Define relational databases

A

Consists of multiple tables linked together. Each table usually represents a ‘thing’ or an entity and the link are their relationships

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8
Q

Define primary key

A

A field that has a unique value for every record in a table

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9
Q

Define foreign key

A

The primary key in one table being used as a field in another table, creating a link

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10
Q

Define secondary key

A

A field by which records are likely to be searched and is therefore indexed

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11
Q

What is OMR

A

Optical Mark Recognition - A data input method that recognises the positions of marks made on paper

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12
Q

What is OCR

A

Optical Character Recognition - A data input method that converts images of text to machine editable text

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13
Q

What is a DBMS

A

Database Management System - Software used to control a database, overseeing amendments to its structure, and used to access and amend the data itself

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14
Q

Examples of DBMS

A

MySQL, Microsoft Access, PostgreSQL

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15
Q

What is SQL

A

Structured Query Language - A language used to find and manipulate data within a database

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16
Q

What is normalisation

A

Normalisation - The process of changing the structure of a relational database to remove the potential for data redundancy

17
Q

What does atomic mean

A

A field that cannot be broken down into multiple smaller field

18
Q

What are the rules for 1NF

A
  • Data in every field is atomic
  • No repeating fields
  • Must have a primary key
19
Q

Define composite key

A

A primary key made of two or more fields

20
Q

What are the rules for 2NF

A
  • In 1NF
  • Every field must only depend on all of the primary key
21
Q

What are the rules for 3NF

A
  • In 2NF
  • No fields must depend on any field other than the primary key
22
Q

Explain SELECT … FROM

A

Used to retrieve specified fields from a specified table

23
Q

Explain WHERE

A

Used to filter the results that are returned

24
Q

Explain LIKE

A

Used with WHERE to select fields that match a given pattern
e.g. WHERE Name LIKE ‘New %’;

25
Q

Explain DELETE

A

Used to delete records
e.g DELETE FROM Customers WHERE forename = ‘Jason’

26
Q

Explain INSERT

A

Adds records into a table
e.g INSERT INTO Cust (forename, surname)
VALUES (‘Jason’, ‘Smith’)

27
Q

Explain DROP

A

Used to delete whole tables
e.g DROP TABLE Customer

28
Q

Explain JOIN

A

Used to combine information. It selects data every time it finds a match between the two specified fields
eg SELECT Subject.Subject, Teacher.Teacher
FROM Subject
INNER JOIN Teacher ON Subject.Teacher_Code = Teacher.Teacher_Code;

29
Q

What is referential integrity

A

Guaranteeing the consistency of a database by ensuring no record points to another record that doesn’t exist

30
Q

What is a transaction

A

A group of actions in a database creating a unit of work

31
Q

What is ACID

A

Atomicity, Consistency, Isolation and Durability. These are concepts that underpin database transactions

32
Q

What is atomicity

A

A change is performed or not performed. Half-finished changes must not be saved

33
Q

What is consistency

A

Databases have sets of rules that must be adhered to by all the data they contain. Transactions should never leave a database in a state where any of these rules are broken

34
Q

What is isolation

A

A running transaction must not be able to be affected by a different transaction.

35
Q

What is durability

A

Once made, transactions cannot be lost. Changes must be written to storage in order to preserve them

36
Q

What does record locking do

A

Prevents anyone accessing a record in use by another person

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