Relational databases and SQL

Transcription

1 Relational databases and SQL Relational Database Management Systems Most serious data storage is in RDBMS Oracle, MySQL, SQL Server, PostgreSQL Why so popular? Based on strong theory, well-understood performance Highly optimized for large data sets (petabytes) Mature, broadly tested tools Broad installed user base and administrative expertise Mature mechanisms for failure recovery (Mostly) standardized data formats and SQL interface

2 Alternatives? Object-Oriented & NoSQL Databases Basically saves and restores objects (or associative arrays) Better fit with code NoSQL has recently gained some real momentum Files Works nicely with javascript-all-the-way solutions RDBMS is just a layer of abstraction over files Think you can do it better? Write your own interface Simpler, more control, no real setup and maintenance Makes sense when you need 1 feature, not 1000 Although probably you re just reinventing the wheel

3 Storing data What kind of data do you store On websites you regularly use? In your phone? How would you store it in tabular form? 2-dimensional data Rows and columns

4 Each table is defined by: Table name List of columns RDBMS tables Each column has a name and a data type Excel, more or less Rows represent entities Columns represent pieces of data about those entities Often called attributes Like a simple array of objects Each row is an object Columns are the members of the object (type, name)

5 Table of albums RDBMS tables Each row is an album Each column is an attribute of albums Good practice to have an integer ID column Id Artist Title 1000 Living Colour Vivid 1001 Dave Matthews Band Listener Supported (disc 1) 1002 The Black Crowes Amorica

6 MySQL Very popular open-source RDBMS Flexible, powerful, scales well Broad base of expertise to draw on Fairly simple to set up (harder to optimize) Not as powerful as Oracle or PostgreSQL Few applications need that kind of power

7 Command line tools: MySQL Tools Connect with a mysql shell mysql u root p Execute a sql file mysql u root p [db] < file.sql Save a database as an sql file mysqldump u root p [db] [tables] > file.sql phpmyadmin in XAMPP Start Apache/MySQL at control panel Point browser at

8 Create a new user Database setup CREATE USER 'user'@'localhost' IDENTIFIED BY 'password'; Create a new database CREATE DATABASE test_db; Give user privileges on the database GRANT ALL PRIVILEGES ON test_db.* TO 'user'@'localhost'; Set active database USE test_db; View tables SHOW TABLES; DESC <some_table>;

9 Structured Query Language (SQL) (Sort of) standard interface to RDBMS Everyone has to go add their own helpful constructs Descriptive language Describes the data, not how to store/retrieve it Allows each RDBMS to implement/optimize how they want SQL queries request information to be stored, altered or retrieved from a RDBMS 3 major query types: SELECT, INSERT and UPDATE

10 Creating a table in a database CREATE TABLE people ( id INT NOT NULL AUTO_INCREMENT PRIMARY KEY, first_name VARCHAR( 64 ) NOT NULL, last_name VARCHAR( 64 ) NOT NULL ); MySQL data types INT (whole numbers) DOUBLE (floating point numbers) CHAR( n ) (fixed-length string) VARCHAR( n ) (variable-length string, max size n)

11 Creating a table in a database CREATE TABLE people ( id INT NOT NULL AUTO_INCREMENT PRIMARY KEY, first_name VARCHAR( 64 ) NOT NULL, last_name VARCHAR( 64 ) NOT NULL ); NOT NULL Column value cannot be NULL PRIMARY KEY A primary key is a unique identifier for a particular row in a particular column Always provides a way to refer to a given row Good to have in all entity tables AUTO_INCREMENT Automatically set the value of this column DB specific We ll revisit this with INSERT

12 Insert data into a table CREATE TABLE people ( id INT NOT NULL AUTO_INCREMENT PRIMARY KEY, first_name VARCHAR( 64 ) NOT NULL, last_name VARCHAR( 64 ) NOT NULL ); INSERT INTO people (first_name, last_name) VALUES( Joe, Smith ); INSERT INTO people (first_name, last_name) VALUES( Jose, Villareal ); You could also specify the id for each row you insert But, AUTO_INCREMENT automatically specifies Id as the last Id + 1