data query

Center for Environmental Studies

Arizona State University

Central Arizona PhoenixLTER

Data Query

Peter McCartney

RDIFS Training WorkshopSevilleta LTER

October 28-30, 2002




Goals

• Retrieve data from storage• Join tables as needed to produce

matrix output (denormalize)• Transform data to meet analytic

needs– Filter, aggregate, select




Structured Query Language

• Universal syntax for querying relational datbases.

• Provides means for specifying– Attributes required– The source tables and how to join

them– Criteria for limiting the result

(filtering)– Instructions for ordering the result set




A Simple SQL QuerySELECT personnel.first_name,

personnel.last_name, personnel.country_code

FROM personnelWHERE personnel.country_code="usa“




A Slightly More Complex Query

SELECT personnel.first_name, personnel.last_name, country.country_name, interests.interest_area

FROM country INNER JOIN (personnel INNER JOIN interests ON personnel.person_ID = interests.person_ID) ON country.country_code = personnel.country_code

WHERE (((personnel.country_code)="usa"))




Result




Views

• Views are query statements that are stored in the database.

• Views return a matrix and may be treated as if they were another table (you can use a view in a query)

• Only the query statement is stored; the result set is reproduced each time you call the view

• Views let you hide much of the complicated table joins from your users




Query a View

SELECT myFirstView.*FROM myFirstViewWHERE

(((myFirstView.interest_area)="data management"));




Querying Remote Databases

• The beauty of relational databases is that you can use a variety of client applications to query them.

• Your users do NOT need to learn Access in order to use your database.




Accessing Databases

• Native protocol– Every database has its own native

protocol. Applications must be written to this.

• Open Data Base Connectivity– Windows, Unix, Mac

• Java Data Base Connectivity– Cross platform– Designed for Java Language




A Typical Client Server Connection

Database(Access)

Application(Excel)

ConnectionLayers(ODBC)

NativeSyntax

StandardSQL

•Connectivity layer translates applications requests into database‘s native syntax.




Define an ODBC Source




Query

• Once an odbc source is defined, you may access it from any application that supports ODBC

• Excel, SPSS, ArcView, MapInfo, Active Server Pages

• Range of capabilities and user friendly features will vary




Query from Arc View




Programming the Web

• Client side– ECMCA languages – Javascript– Code executed by client browser. All data

must be transferred to browser

• Server side– Template “page” scripting– CGI programs




Web Query

• HTTPD/CGI programs– External program receives form input,

generates entire page to be returned.– Server side Java

• Server scripting– Permits embedding script within html pages– Html code is returned as is, script code is

executed by script engine prior to page being returned.

– Active Server Pages (MS IIS)– Java Server Pages ( Apache tomcat, BEA

WebLogic, IBM WebSphere, Allaire Jrun




Three-tiered Query using ASP

• Declare a connection object and at least one recordset object.

• Open the connection to your ODBC source

• Parse the form request parameters • Build an sql query• Execute the query putting the result in

your recordset• Access the data in your recordset and

write html output to display the data in the page




Lab Assignment

• Add some data to your database• Create some views and store them

in your database– (or use the samples at: \\alamillo\

inetpub\wwwroot\dbweb)• Create an ODBC data source• Query your data from Access• Create an asp page to display

some data following templates:• http://alamillo/dbweb

data query

Documents