ชนิดความสัมพันธ์ EXACT กับ SCAN

[kalinaz]

ขอสอบถามเป็นความรู้ครับ ชนิดความสัมพันธ์ EXACT กับ SCAN ตอนเราแก้ไข เชื่อมความสัมพันธ์ Relate File เห็นมันขึ้นเป็น Exact ตลอดเลยอยากรู้ว่า 2 ตัวนี้ต่างกันยังไงครับ แล้วมันใช้กับกรณีไหนได้บ้าง ขอบคุณครับ

[savek]

ขออนุญาตอ้างอิงจากเว็บนี้ครับ

Joining DBF files. When joining DBF tables, joins can be made between the shapefile DBF table and one or more external DBF tables that reside in the same directory as the shapefile. One restriction is that a joined DBF file cannot be another shapefile DBF file that is currently being used in an ArcIMS service.

To join DBF files, the joinexpression attribute is used. This attribute uses the syntax: "To=[master table column which will be used for joining], From=[defines a join table column which will be joined], Type=[exact or scan]".

To Refers to the master DBF table and defines the field that is used for joining. When referring to this table, the DBF table name must be used as a prefix to the field name. The entire expression is surrounded by square brackets, e.g., joinexpression="To=[mastertable.fieldname]".
From Refers to the DBF table that is joined to the master DBF table and the field that is used for joining, e.g., joinexpression="From=[jointable.fieldname]".
Type=[exact] Defines an exact match relation that permits only a single match between the master and join tables. Both one-to-one and many-to-one relations are exact match relations. In a one-to-one relation, there is only one record in the master that matches a single record in the join table. In a many-to-one relation, there are one or more records in the master that match a single join record. If there are multiple join records that match a single master record, then a composite record is only generated for the first join record.
Type=[scan] In a scan relation, if there are multiple join records for a master record, there is one composite record in the extended data file for each of the matching join records. Both one-to-many and many-to-many relations are scan relations. In a one-to-many relation, each record in the master can have multiple matching join records. A many-to-many relation is the same as one-to-many, except that different master records can match the same join record.

http://downloads.esri.com/support/docum ... lquery.htm

[kalinaz]

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