What is a JOIN and how is it handled?
By default the output from each table class contains values which are only from the database table with which it is associated. This output may include calculated fields such as those created by means of CONCAT or a similar function. There may be occasions when it is desired to incorporate values from other database tables, such as to replace a foreign key with a description from the foreign table. In order to gather information from more than one database table it is necessary to perform what is known in the database world as a JOIN, and within this framework a JOIN can be performed in any of the following ways.
