WebFund 2014W Lecture 7: Difference between revisions

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* [http://dl.cuol.ca/capture/Anil.Somayaji/COMP_2406_2014W_Lecture_7_-_20140129_143752_27.mp4 Original from CUOL]
* [http://dl.cuol.ca/capture/Anil.Somayaji/COMP_2406_2014W_Lecture_7_-_20140129_143752_27.mp4 Original from CUOL]


Databases:
== Databases ==
why?
why?
* Persistence - You want to stick around (vs. RAM)
* Persistence - You want to stick around (vs. RAM)
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* columns (fields)
* columns (fields)


Example
== Example ==
=====


Table: People
Table: People
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* Simplest: sorts specific fields in a table (create secondary keys)
* Simplest: sorts specific fields in a table (create secondary keys)


                          Secondary key          Primary key
Secondary key          Primary key
                          ========            =======
========            =======
                          First Name                ID
First Name                ID
                          ---------                --
---------                --
>>                      Anil                          1
Anil                          1
sort                    Dana                        2
Dana                        2
these                  Annie                        3
Annie                        3
alphabetically
 
* sort the names Alphabetically.


Transactions:
Transactions:

Revision as of 16:59, 13 March 2014

The video from the lecture given on January 29, 2014 is available:

Databases

why?

  • Persistence - You want to stick around (vs. RAM)
  • Concurrency in writes - (vs. files)
  • Search - (vs. files)
    • Dynamic data should NOT be stored in files.

SQL(Structured Query Language) vs. NoSQL

  • SQL makes queries to databases, assuming queries are highly structured.
  • for relational databases.

What is a structure of a relational database? e.g. Tables - relations connect fields between tables

  • rows (records)
  • columns (fields)

Example

Table: People

ID First Name Last Name Phone Email 1 Anil Somayaji 555-1212 soma@scs.carleton.ca 2 Dana Somayaji 555-1212 dana@example.ca (should check whether it is a valid address)

Validation Problem:

  • Where to check for bad data?
  • Can do on:
    • Web client (helpful)
    • Web server (must)
    • Database (useful)

Example continued:

Table: Invoices

Inv. ID Description Amount Customer 1 iPad $700 1 <- Which is Anil in the People table) 2

  • One relation: Invoice = Customer ID -> People ID

Could ask for simple queries:

  • All records in People with first name == Anil
  • Which customer has spent the most in our store?
    • Sum of all invoices for each customer
    • find max

Indexing:

  • Simplest: sorts specific fields in a table (create secondary keys)

Secondary key Primary key

== =

First Name ID


--

Anil 1 Dana 2 Annie 3

  • sort the names Alphabetically.

Transactions:

  • What if I want to change records in multiple tables in a coordinated fashion?
  • Airline example
    • Reserve seat
    • Pay
    • Commit: check that payment and reservation both worked first

NoSQL Databases: No transactions, no real relations