Geographic Information Systems Using ESRI ArcGIS 9.3 Complex selection by attributes

SQL The “language” used to select objects by attribute is called SQL (Standard Query Language). A wide literature on its use is freely available.

SELECTION by attribute Logical Operators It is possible to connect conditions with AND / OR logic operators, making a complex query

SELECTION by attribute Logical Operators AND Connects two conditions: the object is selected if both the conditions are true e.g. “TYPE” = 15 AND “NAME” >= “G” same results of the method “select from current selection”

SELECTION by attribute Logical Operators OR Connects two conditions: the object is selected if at least one of the conditions is true e.g. “TYPE” = 15 OR “NAME” >= “G” same results as the method “Add to current selection”

SELECTION by attribute Parentheses The use of parentheses allows to create complex queries e.g. (“TYPE” =13 OR “TYPE”=14) AND “NAME”>’G’ is different from “TYPE” =13 OR (“TYPE”=14 AND “NAME”>’G’)

SELECTION by attribute Verify It is possible to verify the sintax of complex queries before running them. Useful only for very complex queries, since when they run it may take a long time before an error is detected

SELECTION by attribute Save / Load It is possible to save queries and to load them. This is useful for queries that are to be repeatedly used more than once on different datasets