Chapter 3 Building Physical Diagrams

Defining reference joins

A join is a link between a column in a parent table and a column in a child table (column pair) that is defined within a reference.

A join can link primary key, or alternate key, and foreign key columns, or user specified columns in the parent and child tables that are independent of key columns.

Default joins at reference creation

When you create a reference, the current selections for Model Options determine the creation of the following types of default joins:

• Joins that link primary and foreign key column pairs
• Joins that are linked to primary key columns, but are not linked to child table columns, so are incomplete
• No joins created

Join creation is determined by the following selections for Model Options:

Linking columns in a primary or alternate key

For any reference you can choose to link a primary key, or alternate key, to a corresponding foreign key. When you select a key from the Joins page of the reference property sheet, all the key columns are linked to matching foreign key columns in the child table.

Reuse and Migration option for a selected reference

You can use the following buttons on the Joins page to reuse or migrate columns linked by joins.

Button	Name	Description
	Reuse Columns	Reuse existing child columns with same code as parent table columns
	Migrate Columns	Migrate key columns to foreign key columns. If columns do not exist they are created
	Cancel Migration	Delete any migrated columns in child table

Auto arrange join order

The join order can be established automatically or manually by using the Auto Arrange Join Order check box. The Auto Arrange Join Order check box is grayed if the reference is not joined to a key.

Selecting or clearing the Auto arrange join order check box has the following effects:

To define joins in a reference:

1. Double-click a reference in the diagram to display the reference property sheet.
2. Click the Joins tab to display the Joins page.
3. Select a key from the Parent Key dropdown listbox to create joins between primary key, or alternate key, and foreign key columns.
   
   or
   
   Select <NONE> from the Parent Key dropdown listbox to create joins between user-specified columns. If you select <NONE>, the column lists are empty.
   
   The columns linked by the joins are listed in the Parent Table and Child Table columns. A Joins page with a selected Parent Key is shown below:
   
   
   
      Changing a foreign key column linked by a join
   You can change the foreign key column linked by a join by clicking the column in the Child Table list, and selecting another column from the dropdown listbox.
   
   
   
   
4. <Optional> If you selected <NONE> from the Parent Key dropdown listbox, click the Parent Table Column and select a column from the dropdown listbox, then click the Child Table Column and select a child column.
5. <Optional> Select or clear the Auto arrange join order check box.
   
   A Joins page with a selected parent key and selected Auto arrange join order check box is shown below:
   
   
   
      Enabling the Auto arrange join order check box
   To enable this check box, add an EnableChangeJoinOrder item to the Reference category in the DBMS definition file and set the value to YES.
   
   
6. Click OK.

For information on adding an item to the Reference category, see chapter DBMS Reference Guide in the Advanced User Documentation .

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