Overview

A database table join links two database tables together so that their records are synchronized. A join has a “master” table and a “slave” table. The master table controls the slave table. As you move from row to row in the master table the slave table(s) will also move in a coordinated fashion.

A join consists of a master table and slave table linked by two columns common to both tables. There does not need to be a one-to-one correspondence of values in the columns (fields). However, if the slave table contains duplicate values in its “key” column then which row will be selected when the master table's key column is at that value is not certain.

Basic Characteristics

  • A master can have an unlimited number of slaves.
  • A slave can have only one master.
  • Daisy-chaining is allowed: A slave can also be a master over other tables.
  • When the master table goes off record, so does the slave.
  • When there is no corresponding row in the slave table, the slave table will go off record (to a “no-data” state).
  • When there are multiple matching records in the slave table, the chosen row in the slave table is undetermined.

GeoNetWeaver Concerns

GeoNetWeaver expects the topmost master table to be a shapefile and also control all other tables.

Any tables that are not controlled by the topmost table will effectively not contribute to the geoproject.

netweaver/windows/database_table_joins.txt · Last modified: 2009/05/11 20:32 (external edit)
 
Recent changes RSS feed Donate Powered by PHP Valid XHTML 1.0 Valid CSS Driven by DokuWiki