DAY 9: DATABASES Rohit February 17,

DATABASES A database is an organized collection of data There are many types of databases –Flat File –XML –Workbooks –Relational –Key-Value Store 2

POPULAR DROP-OUT BILLIONAIRES (IMPORTANCE OF COMPUTER SKILLS) 3

WHY LEARN THESE SKILLS? Database skills are an essential part of basic computer skills like Programming.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. 4

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). 5

WHERE ARE DATABASES USED? 6 Source: oracle.com

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 7

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 8

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 9

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 10

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” 11

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 12

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 13

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 14

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 15

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’ 16

COMMON EXCEL ISSUES Switch Row/Column Merge (but not center) Relative/Absolute/Mixed References 17