Copyright © 2006 by Maribeth H. Price 6-1 Chapter 6 Queries

Copyright © 2006 by Maribeth H. Price

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Chapter 6

Queries


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Outline

• Understanding queries and how they are used• Knowing how to select features interactively

using a variety of methods• Selecting features using SQL queries on their

attributes• Selecting features based on their spatial

location with respect to other features• Using Definition Queries to create subsets of

data layers


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What are queries?

• Extract certain records from a map or table

• Records meet certain criteria– Aspatial queries

• All parcels with value greater than $100,000.

– Spatial queries• All parcels that lie completely within the flood plain


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Selected features

Highlighted in tableHighlighted in map

States for which POP2000>2 million


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Types of Queries

• Interactive selection– Choose features by pointing to them on the

screen

• Select By Attribute– Select features based on attribute criteria

• Select By Location– Select features based on their spatial

relationships


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Interactive Selection

Select Features tool

Click on feature to select

Hold down shift key to select more than one feature

Draw a rectangle that passes through features to be selected.


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Selectable LayersStates selectableAll layers selectable


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Selection options


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Clear SelectionOn toolbar

From table options menu From main menu


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The Selection tab

Right-click entry for context menu

You can also make layers selectable here by checking them

This one clears features only for this layer


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Selection logic

• No selection– All features exported

• No selected features– No features exported

• Selected features– Only selected features

exported

Example: Exporting features to a new shapefile


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Two ways to select features

• Selecting by Attribute– Queries based on one or more fields in the

table• Find all wells with chloride concentration > 100ppm

• Selecting by Location– Queries based on the relationship of features

to another layer• Find all wells that lie inside industrial parcels


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Select By Attribute

Some Valid Queries

SELECT *FROM cities WHERE "POP1990" >= 500000

SELECT *FROM counties WHERE “BEEFCOW_92” < “BEEFCOW_87”

SELECT *FROM parcels WHERE “LU-CODE” = 42 AND “VALUE” > 50000

SELECT *FROM rentals WHERE “RENT” > 700 AND “RENT” < 1500

Note: Shapefile tables use quotes for field names; geodatabase tables use brackets


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The Like Operator

• “NAME” LIKE ‘%(D)%’ – Finds all of the (D)

Democrats

• % is wildcard• Ignores Don or Danforth

• “NAME” LIKE ‘%New %’ – Would find New Hampshire

and New York, but not Newcastle or Kennewick


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Boolean expressions

A AND B

A XOR B A NOT B

A OR B

A B

0

1

Blue circles represent areas where condition holds

(True) = 1


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AND vs OR

“Land-use” = ‘RES’ AND

“Land-use” = ‘COM’

“Land-use” = ‘RES’ OR

“Land-use” = ‘COM’

“Pop2000” ≥ 5000 OR

“Pop2000” < 9000

“Pop2000” ≥ 5000 AND

“Pop2000” < 9000

Wrong Right

Remember—you test each feature separately


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Multiple conditions

• Use parentheses to enforce order of evaluation

(“LU” = ‘RES’ or “LU” = ‘COM’) and “Value” > 100000

“LU” = ‘RES’ or (“LU” = ‘COM’ and “Value” > 100000)

$75,000

$125,000

$75,000

$125,000

$75,000

$125,000

$75,000

$125,000

RES COM


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Select By Location

Select counties that completely contain state capitals

Select counties that are within 200 miles of Denver


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Select By Location

Select counties that intersect rivers

Select rivers that intersect Texas


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Select By Location

Select cities that are within 20 miles of an interstate highway

Select cities that are completely within counties named Washington


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Selecting by location


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Intersect


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Within distance of


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Using a selected set


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Within the same layer


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Selection methods

Available for all three types of selection


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Applying selection methods

Create new selection: hearts = yellow

Add to current selection: hearts = red

Add to current selection: hearts = blue

Remove from selection: hearts = red

Select from selection: hearts = blue

Select from selection: hearts = orange


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Select from currentCities within 50mi of earthquakes

Having > 500,000 people


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Creating layers

• Common operation following a query• Creates a layer file


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Creating layers


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Exporting selections

Creates new shapefile


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Definition Queries

• Redefine a layer to include a subset of the actual features

• Only selected features appear on map and in table

• Has no effect on data stored on disk• Temporarily treats a layer as being smaller

than it actually is• Does not require an additional data set to

be stored.


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Documents

Copyright © 2006 by Maribeth H. Price 6-1 Chapter 6 Queries