1.3.2 Databases Flashcards

1
Q

Database

A

An organised collection of data

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2
Q

Database advantages

A

Make data available to users, the data is correct and the data can be held securely

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3
Q

Table

A

A collection of associated data stored within a database

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4
Q

Fields

A

The characteristics of each table

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5
Q

Record

A

An individual entry that belongs in a table

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6
Q

Entity

A

Something in the real world that we store data about

Becomes a table in a database

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7
Q

Attribute

A

A characteristic of an entity

Becomes a field in a database

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8
Q

Entity description format

A

TableName(Entity1, Entity2…)

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9
Q

Char(n) vs VarChar(n)

A

A char string has fixed length n, a varchar string has variable length up to n

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10
Q

How to access a database

A

Using a DBMS (Database Management System)

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11
Q

Flat file database

A

A database comprised of a single table, based around a single entity and its attributes

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12
Q

Flat file advantages and disadvantages

A

+ simple and quick to set up

- very inefficient, used for storing small amounts of data

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13
Q

Relational databases

A

Databases split into multiple tables linked by relationships

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14
Q

Primary key

A

A field in a record which is unique, allowing each record to be uniquely identified. Must not be duplicated or reused.

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15
Q

Secondary key

A

A field can be defined as a secondary key to be indexed for faster lookups.

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16
Q

Foreign key

A

The key in a table that correlates to a primary key in another table

17
Q

Entity Relationship Diagrams (ERD)

A

One to one is linked by a straight line
One to many diverges into 3 near the many side]
Many to many diverges into 3 at both ends

18
Q

SQL

A

Structured Query Language

A declarative language used for querying and updating tables in a relational database

19
Q

SQL Queries

A

Retrieves data based on a given criteria

20
Q

SQL Clauses

A

Filters data and returns data that fulfils a specific condition

21
Q

SQL Predicates

A

Specify conditions which return the filter

22
Q

SQL Expression

A

A combination of one or more values, functions and operators

23
Q

SQL Select format

A

SELECT lists the fields to be displayed
FROM states which table they come from
WHERE specifies a condition
ORDER BY lists how they are sorted (ASC,DESC)
e.g. SELECT name FROM sales WHERE cores=4 ORDER BY name DESC

24
Q

SQL UPDATE

A

Modifies existing values in a table

25
SQL DELETE
Deletes existing records from a table
26
SQL DROP
Deletes a database or table | DROP table tableName
27
SQL INSERT INTO
Inserts new records into a table | INSERT INTO Table(Fields), VALUES (Data)
28
Join
Combines rows from 2 or more tables based on a related column between them
29
INNERJOIN
The SQL for joining tables | INNERJOIN newTableName on table.field = table.field
30
SQL UPDATE Syntax
UPDATE tableName SET field = newValue WHERE …
31
SQL Additional Data Types
TIME and CURRENCY
32
SQL Select All
SELECT *
33
SQL Like
Like "%xx%" | Where the string xx is included anywhere in the data it is returned