Virtually Join Data Tables
Virtual Join links a main data table to one or more auxiliary data tables. This feature enables the main data table to access data from the auxiliary data tables without physically joining the tables. Virtually joining tables saves memory, because the same data are not replicated in every table that references them. And updating linked data is simpler; linked data can be independently updated in the source table without being updated in the referencing table.
The Link ID and Link Reference column properties make the linking possible.
• The Link ID column property marks a column in the auxiliary data table as the ID column. That is, the rows of the data table are uniquely identified by the values of the ID column. The data table that has a Link ID column property is referred to as the referenced data table.
• The Link Reference column property links a column in the main data table to the Link ID column in the referenced data table. The column property specifies the path name of the referenced data table. The column that has a link reference is referred to as the referencing column. The referencing column can look up the data of the auxiliary data tables through the Link ID column.
Figure 6.36 shows an example of virtually joined data tables. Pizza Profiles.jmp is the referenced data table because the ID column contains a Link ID column property. The ID column contains unique values that correspond to data in the referencing data table, Pizza Responses.jmp.
Figure 6.36 Virtually Joined Data Tables
Note: A column can have a Link Reference column property, but it does not necessarily have to link columns from the referenced data table. The virtual join icon next to the column in the Columns list is gray 
. This can happen if the referenced data table is not opened or the referencing column is excluded. See Virtual Join Icons in the Get Started section for more information about the other virtual join icons.
With the link column properties set up, all columns from the referenced data tables become part of your main data table. Therefore, if the main data table has a referencing column, the columns of the referenced table automatically appear in the Select Columns list of the launch window.