DAY 12:DATABASES

RAHUL KAVIRahul.Kavi@mail.wvu.eduOctober 3, 2013

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LAST CLASS

• Two Variable What-If Analysis• Goal Seek• Scenario Manager• Solver• 3D Formulas• Templates• Cell Styles

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DATABASES

• A database is an organized collection of data

• There are many types of databases– Flat File– XML– Workbooks– Relational– Key-Value Store

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POPULAR DROP-OUT BILLIONAIRES (IMPORTANCE OF COMPUTER SKILLS)

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WHY LEARN THESE SKILLS?• Database skills are an essential part of basic

computer skills like Programming.• Limitless possibilities with a 800$ computer from

the comfort of home (consume or produce).• Create own website/blog (commercial,

personal).• Computer skills like Programming, Database

Management, Blogging are like culinary skills.• Business Plan competition.

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WHERE ARE DATABASES USED?

• Storing bank records, corporate data, etc.• Storing login credentials for websites/blogs.• Store content of popular websites like

Flickr.com, YouTube.com, etc.• Store content of popular services like

Netflix, Instagram,Pandora, iTunes, Spotify, Game Center (iOS), App Store, Play Store (Android App Store).

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WHERE ARE DATABASES USED?

Source: oracle.com

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RELATIONAL DATABASES

• Access is a relational database– A relational database is a collection of data

items organized as a set of formally described tables from which data can be accessed easily

– In addition to table definitions, there are also relationships between tables

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RECORDS AND FIELDS REVIEW

• A single entry in a table is called a “record”– A record (row) is one or more pieces of data about a

single entity• Each piece of data in a record is a “field”

(column).• A table definition lists all the fields the records in

that table have– The definition can define default values for fields– Some fields are required for each record, others are

optional

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KEYS

• Each table has to have a “primary key”. This is a field, or a combination of fields that will be unique to each record

• Keys allow you to identify a particular record

• You can use the key in other tables to reference the record

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INDEXES

• Indexes are an ordering of a key or other field that is computed on creation and kept up to date as the database is updated

• By using the index, the database software is able to quickly retrieve the record given the field value

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RELATIONSHIPS

• By including a the key from one table as a field in a different table, we create a relationship between the two tables

• This allows us to link the data between two tables

• In the second table, the field is known as a “foreign key”

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EXAMPLE

• Two tables: People, PhoneNumbers– People: id, first_name, last_name, birthdate– PhoneNumbers: id, country_code, area_code,

number, person_id• PhoneNumbers.person_id would hold the

same value as People.id for phone numbers that belong to the given person

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CASCADING

• If the records with the foreign key are only used as an extension of the original table, you may want to cascade updates and/or deletes– Deletes: If the original record is deleted, the

foreign key record is deleted– Updates: If the key of the original record is

changed, the foreign key is updated to match

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PLANNING DATABASES

• Define what tables you need• Define what fields belong in each table• Define what data types each field should

be• Define default values for each field• Choose between required and optional

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NORMALIZATION

• Normalization is a process of organizing fields and tables to minimize redundancy of data– DRY (don’t repeat yourself)– If you repeat yourself, when you need to

make a change you have to change it everywhere or you will have problems

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SQL• SQL is structured query language• SQL is how Access interacts with data under the

hood• INSERT INTO ‘table’ (‘field1’, ‘field2’) VALUES

(‘value1’, ‘value2’)• UPDATE ‘table’ SET ‘field1’ = ‘value1’ WHERE

‘field2’ = ‘value2’• DELETE FROM ‘table’ WHERE ‘field’ = ‘value’• SELECT ‘field1’ FROM ‘table’ WHERE ‘field2’ =

‘value’

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COMMON EXCEL ISSUES

• Switch Row/Column• Merge (but not center)• Relative/Absolute/Mixed References