Click the Operator down arrow and select a join operator from the drop down list Edit the join name, description, and join conditions as required.

10-20 Oracle Fusion Middleware Administrators Guide for Oracle Business Intelligence Discoverer Figure 10–14 Edit Join dialog: Options tab

4. Edit the join options as required.

5. Click OK to save any changes you have made and close the dialog.

To view or edit join properties using the Join Properties dialog: How to edit a join using the Join Properties dialog You might want to edit a join using the Join Properties dialog.

1. Select a join on the

Workarea: Data tab and choose Edit | Properties to display the Join Properties dialog . Figure 10–15 Join Properties dialog: General tab Tip : You can select more than one join at a time by holding down the Ctrl key and clicking another join. All properties that are common to each selected join are Creating and Maintaining Joins 10-21 displayed. If the value of a property is not common to all of the selected joins, the Value field is blank. 2. Make changes as required. 3. Click OK to save any changes you have made and close the Join Properties dialog. How to delete a join You might delete a join when it is no longer required. For example, you might want to prevent end users creating a worksheet that contains items from two previously joined folders. Note: When you delete a join, other EUL objects for example, complex folders that use the join might also be affected. It is recommended that you export the EUL before you attempt to delete a join. To delete a join:

1.

Select a join on the Workarea: Data tab and choose Edit | Delete to display the Confirm Delete dialog . Tip: You can select more than one join at a time by holding down the Ctrl key and clicking another join. 2. optional To see the objects that might be affected by deleting this join: a. Click Impact to display the Impact dialog . Figure 10–16 Impact dialog The Impact dialog enables you to review the other EUL objects that might be affected when you delete a join. Note: The Impact dialog does not show the impact on workbooks saved to the file system that is, in .dis files.

b. optional Select a row in the Impact dialog to view text at the bottom of the

list, indicating what affect the current action will have on the EUL object.

c. Click Close to close the Impact dialog when you have finished reviewing the

impact of deleting the join. 10-22 Oracle Fusion Middleware Administrators Guide for Oracle Business Intelligence Discoverer 3. Click Yes if you still want to delete the selected joins. What are fan traps, and how does Discoverer handle them? A fan trap is a group of joined database tables that might return unexpected results. The most common manifestation of a fan trap occurs when a master table is joined to two or more detail tables independently. Figure 10–17 A simple fan trap schema Although this construction is relationally correct, you are likely to return incorrect results if you use a straightforward SQL statement to aggregate data points. However, if you use Discoverer to aggregate the data points, Discoverer will never return incorrect results, provided fan trap detection is enabled. Every query that Discoverer generates is interrogated for potential fan traps. If a fan trap is detected, Discoverer can usually rewrite the query using inline views to ensure the aggregation is done at the correct level. Discoverer creates an inline view for each master-detail aggregation, and then combines the results of the outer query. For an example of how Discoverer will return correct results when a straightforward SQL statement will return incorrect results, see Example of a fan trap . In some circumstances, Discoverer will detect a query that involves an unresolvable fan trap schema, as follows: ■ if the detail folders use different keys from the master for the join ■ if there is a direct join relationship between the detail folders thereby creating an ambiguous circular relationship ■ if non-aggregated values are chosen from more than one of the detail folders ■ if more than one detail folder has a separate join relationship to a different master folder In the above circumstances, Discoverer disallows the query and displays an error message. In addition, Discoverer controls which columns can be totalled. If a worksheet displays values of items from both the master folder and the detail folder, Discoverer will not total the values together. Instead, Discoverer will display a null to prevent incorrect or unexpected results. For more information about enabling or disabling fan trap detection in Discoverer, see the Oracle Fusion Middleware Users Guide for Oracle Business Intelligence Discoverer Plus. Example of a fan trap Consider an example fan trap schema that includes a master folder ACCOUNT and two detail folders SALES and BUDGET, as shown below: