An introduction to SQL 1/21/2014 – See chapter 2.3 and 6.1 PostgreSQL Acknowledgement – Thanks to Dr. Mayfield for the lab activity.

SQL Query language Divided into “clauses” each of which does a particular piece of work. Two kinds of languages DDL – Data Definition Language – Manipulates the database schema DML – Data Manipulation Language – Manipulates the database data

DDL (2.3) CREATE – Makes new database objects CREATE TABLE … CREATE USER … CREATE DATABASE … ALTER – Changes database objects ALTER TABLE …

DML – 6.1 SELECT – Read only query to examine data from the database. May be used in conjunction with update statements. UPDATE – Update existing data INSERT – Insert new rows DELETE – Delete existing rows

Important clauses SELECT – Chooses the individual fields (columns) from the database (not necessarily a particular table) FROM – Chooses which table(s) we are working with WHERE – Provides criteria for the selection

PostgreSQL Relational DBMS use SQL but each has their own dialects and supported features. PostgreSQL is: “PostgreSQL is a powerful, open source object-relational database system. It has more than 15 years of active development and a proven architecture that has earned it a strong reputation for reliability, data integrity, and correctness.” (

Our server db.cs.jmu.edu Accessible from JMU networks only Hardware 2*12 Core Opteron 2.2 GHz 48 GB RAM (plus 48 GB swap) 6*275 GB Disks (1.5 TB free) Software Linux 3.8 (Ubuntu ) PostgreSQL 9.1

Additional server For those interested in exploring MySQL it is available on: daisy.cs.jmu.edu See me if you want an account.

Logging in From the command line: psql -h db.cs.jmu.edu -U username To change your password: \ password Your db account is separate from your JMU account! Do it now

Create a table using DDL CREATE TABLE movie ( id integer, title text, year integer, genres text, mpaa text, budget text ); White space does not matter but style dictates indentation for readability. Case does not matter for the keywords like CREATE and TABLE but convention has us capitalize them. Do it now!

Loading the db Choices – You can hand enter the data …. OR – You can load it from a file. Today we will load from a file.

Load the database Download About 1.4 MB Uncompress gunzip movies.csv.gz Now 3.8 MB With psql \copy movie FROM movies.csv WITH CSV HEADER; ANALYZE VERBOSE movie; 63,508 rows NOTE: \ is an escape which says to do this outside of psql

Basic psql commands General \? help on psql commands \h: help on SQL syntax \i execute commands from file \q: quit psql (or Ctrl-D) Browsing \d: list tables, views, etc \d NAME: describe table, NAME,/etc Important Ctrl-C cancels the current query Tab completion is your friend!

Your first DML query SELECT title -- what you want from the db FROM movie-- the table to operate on WHERE year = 2012;-- the criterion Use up/down arrows and page up/down g or G: go to first / last line / or ?: search forward / backward Press ‘h’ for help Press ‘q’ to quit

Explore Write another query that includes more than one field in the select and a different criterion. You can use AND and OR to combine criteria. Multiple fields are separated by commas in the SELECT statement.

Homework Download any data set from: Create the table Import the data into your database Write several queries exploring the data set. See HW03 in Canvas