地理信息系统chap08.ppt

8.2 Attribute Data Query 8.2 Attribute Data Query 8.2 Attribute Data Query 8.2 Attribute Data Query 8.3 Spatial Data Query 8.3 Spatial Data Query * Attribute data query requires the use of expressions, which must be interpretable by a GIS or a database management system. ArcGIS uses SQL (Structured Query Language) for query expressions. SQL is a data query language designed for relational databases. IBM developed SQL in the 1970s, and many commercial database management systems such as Oracle, Infromix, DB2, Access, and Microsoft SQL Server have since adopted the query language. A new development is to extend SQL to object-oriented database management systems and to spatial data. Smith P104 Costello P103 Jones P102 Smith P102 Chang P101 Wang P101 Owner_name PIN Residential 1 1.0 7-30-78 P104 Commercial 2 2.5 3-7-97 P103 Commercial 2 3.0 10-6-68 P102 Residential 1 1.0 1-10-98 P101 Zoning Zone_code Acres Sale_date PIN Relation 1: Owner Relation 2: Parcel Example 2: Query parcels that are larger than 2 acres and are zoned commercial. select Parcel.PIN from Parcel where Parcel.Acres 2 AND Parcel.Zone_code = 2 Smith P104 Costello P103 Jones P102 Smith P102 Chang P101 Wang P101 Owner_name PIN Residential 1 1.0 7-30-78 P104 Commercial 2 2.5 3-7-97 P103 Commercial 2 3.0 10-6-68 P102 Residential 1 1.0 1-10-98 P101 Zoning Zone_code Acres Sale_date PIN Relation 1: Owner Relation 2: Parcel Example 3: Query the sale date of the parcel owned by Costello. select Parcel.Sale_date from Parcel, Owner where Parcel.PIN = Owner.PIN AND Owner_name = ‘Costello’ Query Expressions, or the where conditions, consist of Boolean expressions and connectors. A simple Boolean expression contains two operands and a logical operator. Parcel.PIN = ‘P101’ In this example, PIN is the name of a field, P101 is the field value used in the query, and the expression selects the record that has the PIN value of P101. operands logical operator Operands may be a