PostgreSQL/PostGIS: Introduction

Transcription

1 PostgreSQL/PostGIS: Introduction

2 Introduction PostgreSQL A standards-compliant SQL-based database server with which a wide variety of client applications can communicate Server software generally, but not always, runs on powerful computers dedicated for exclusive use to running the business application. Client software on the other hand generally runs on common PCs or workstations. Clients get all or most of their information and rely on the application server for things such as configuration files, stock quotes, business application programs, or to offload computer-intensive application tasks back to the server in order to keep the client computer (and client computer user) free to perform other tasks.. - Wikipedia (4/3/2006) 2

3 Introduction PostGIS An implementation of the OGC Simple Features for SQL Specification within PostgreSQL for the storage of geospatial data (points, lines, polygons) within an SQLbased relational database management system (RDBMS). Developed as a set of functions and data types that spatially enable the PostgreSQL object-relational database system. An open source project developed by Refractions Research (Victoria, BC) Technology analogous to ArcSDE (vector data component) and Oracle Spatial. 3

4 Capabilities PostgreSQL Fully-functional object-relational database that complies with the SQL standard Stored procedures Triggers Custom data types Multiple supported scripting languages Broad programming support for interaction Broad availability of supporting database drivers (including ODBC drivers for Windows platforms) Supported on multiple hardware and software platforms 4

5 Capabilities PostGIS Geodatabase that supports the storage of vector data in compliance with the OGC simple features specification Enhanced geometry storage in support of 4D features Spatial Reference System support and conversion Spatial query capabilities Relationship: distance, equivalence, intersection, crossing, within, overlapping, containment Geometry Processing: area. length, centroid, point-onsurface, boundary, buffer, convex hull, intersection, difference, union, editors, creators Accessors: text, binary, SRID, dimension, envelope, characteristics 5

6 Important References When working in PostgreSQL/PostGIS, there are important references that you will want to have close at hand: The documentation for the PostgreSQL database server. The online documentation for various versions of PostgreSQL may be found online: The documentation for the PostGIS extensions to PostgreSQL. Available as a downloadable PDF file and online from Refractions Research We will only scratch the capabilities of PostgreSQL and PostGIS in the next couple of lectures. The full capabilities of these combined tools only become fully apparent with use. 6

7 Installation of PostgreSQL/PostGIS Detailed installation instructions for PostgreSQL and PostGIS are provided for each of the platforms for which it is available. Two options are generally available for installation: Installation of precompiled binary files for your platform Compilation of the server and geospatial extensions from scratch. If you are working on a Microsoft Windows platform, you will probably want to install precompiled Windows binary files. The Windows binary installers for both PostgreSQL and PostGIS are available for download from the class website. Installation instructions are also available on the website. Brief information relating to linux installation is found in the resources discussed in Hack #87 in the Mapping Hacks text. 7

8 Database Concepts Key concepts that are critical to successful work in the clientserver database environment: All interaction with the server is through the execution of commands in Structured Query Language (SQL) Different client interfaces provide alternative tools for generating and submitting SQL to the server for action Graphical User Interfaces translate your interactions with the interface into SQL which is submitted to the server Text interfaces allow you to directly enter SQL for submission and execution on the server Client interfaces may access a server on the same system as the client, or may interact with remote, networkconnected, servers. Database servers can support multiple concurrent requests 8

9 Examples of Client Interfaces Client interfaces to PostgreSQL include: Programs that support the ODBC and JDBC driver standards (i.e. MS Access, Excel, OpenOffice) Cross-platform, PostgreSQL-specific client interfaces (i.e. pgadminiii, EMS PostgreSQL Manager) Multi-database client applications (i.e. Aqua Data Studio, Navicat) Web-based clients (i.e. phppgadmin, Webmin) Database drivers implemented in various programming/ scripting languages (i.e. PHP, Perl, Python) This diversity of client interfaces provides great flexibility in how the content of PostgreSQL databases are accessed. For example, data may be entered using MS Access, may be analyzed using R, and mapped using GRASS, with all three applications accessing the same, high-performance database. 9

10 Relational Data Model SQL (pronounced Sequel) came out of the ideas proposed by Dr. Edgar Codd in his 1970 paper: A Relational Model of Data for Large shared Data Banks, which described the fundamental concepts of the relational data model. Early SQL databases were developed at UC Berkeley, IBM, and by Relational Software, Inc. (now Oracle Corporation). Relational data models define data structures in which collections of attributes are broken down into tables of values that are related to each other through common key values. Through the process of normalization the tables that comprise a database are defined to eliminate redundancy, and maximize efficient storage and retrieval. 10

11 Relational Data Model address_l1 address_l2 address_city address_state lat lon h_uid Households Address Line 1 Address Line 2 Address City Address State Latitude Longitude Unique ID firstname lastname age sex p_uid h_uid Persons First Name Last Name Age (yrs) Sex (m f) Unique ID Household ID Households Persons 11

12 Relational Data Model - SQL A simple SQL statement allows for the combination of data from these tables into a single combined representation: SELECT address_l1, address_l2, lat, lon, firstname, lastname, p_uid FROM households, persons WHERE persons.h_uid = households.h_uid This combined result represents a merging of the specified columns based upon the matching primary key of h_uid. This query represents a one-to-many relationship between tables. 12

13 SQL The implementation of SQL in PostgreSQL includes 109 commands that allow for the creation, modification, and destruction of all components in the database. Key commands that we will review include: Commands to create database objects CREATE DATABASE CREATE TABLE CREATE VIEW CREATE INDEX 13

14 SQL Commands to alter existing database objects ALTER DATABASE ALTER TABLE ALTER INDEX INSERT UPDATE Commands to destroy existing database objects DROP DATABASE DROP TABLE DROP VIEW DROP INDEX And, most importantly, a command to query the database SELECT 14

15 SQL Examples Creation of a new table within the current database: CREATE TABLE households ( address_l1 character varying(100), address_l2 character varying(100), address_city character varying(100), address_state character(2), lat real, lon real, h_uid integer NOT NULL ); 15

16 SQL Examples Insertion of records into the newly created table INSERT INTO households VALUES ('123 Main St.', 'Apt. 4', 'Sunnydale', 'XZ', , , 1); INSERT INTO households VALUES ('456 Vine Blvd.', '', 'Pescaville', 'MY', , , 2); INSERT INTO households VALUES ('78844 J Street', '', 'Marydale', 'BY', , , 3); 16

17 SQL Examples Selecting records from the database SELECT * from households; SELECT address_city, lat, lon from households; SELECT address_city, lat, lon from households WHERE h_uid = 3 17

18 SQL Examples More database query examples SELECT address_city, lat, lon from households ORDER BY address_city SELECT address_city, lat, lon from households WHERE lat > 36 ORDER BY address_city SELECT address_city, lat, lon from households WHERE lat > 36 AND lon <

19 SQL Examples SQL supports a large number of functions for modifying field values that are returned by a query SELECT address_city, round(lat) as lat, round(lon) as lon from households SELECT avg(lat) as lat_avg, avg(lon) as lon_avg from households SELECT (lat + lon)/3 as gibberish from households 19

20 SQL Views Views within the database allow for the creation of named SQL select commands that are stored in the database that may be later treated like virtual tables. CREATE VIEW combo AS SELECT address_l1, address_l2, lat, lon, firstname, lastname, p_uid FROM households, persons WHERE persons.h_uid = households.h_uid; SELECT * from combo; 20

21 SQL Where Clauses The WHERE clause appears in several SQL commands and should be understood, both for managing data in the database, and for use in external applications like GRASS and MapServer. Things to remember WHERE clauses consist of one or more logical tests that determine which records in the database will be returned or processed. Tests may be combined with the standard operators: AND, OR, and NOT Tests usually include one of the following comparison operators: <, >, <=, >=, =, and <> or!=. 21