Understanding Joins: Outer joins and cross joins often result in large intermediate result sets. This can slow down query performance due to the increased data processing required.

Outer Joins: These include rows that do not have matching keys in the joined tables, which means more data to process and potentially more I/O operations.

Cross Joins: These produce Cartesian products of the involved tables. If the tables are large, the resulting dataset can be enormous, leading to significant performance degradation.

Cognos Documentation: The IBM Cognos Analytics V11.1.x documentation advises optimizing join conditions and limiting the use of complex joins such as outer and cross joins to enhance performance.

Query Performance: Enhancing query performance involves various optimization techniques.

Avoid Functions in Filters: Using functions in filters can lead to slower query performance because functions often require additional computation and can prevent the database from using indexes efficiently.

Best Practices: It is recommended to simplify filters and avoid complex functions to ensure queries run faster.

Reference: IBM Cognos Analytics V11.1.x documentation suggests avoiding the use of functions in filters as a best practice for improving query performance.

To modify a prompt in a relational sourced report to support multi-select functionality, make the following changes:

Change Prompt Property Usage to Select-many:

Edit the Prompt: Select the prompt object in the report.

Property Panel: In the properties panel, change the "Usage" property from "Select-one" to "Select-many". This allows users to select multiple values in the prompt.

Update Filter Expression:

Edit Query: Open the query associated with the prompt.

Change Filter Expression: Modify the filter expression from using "=" to "in". This change ensures that the filter can handle multiple values selected by the user.

These modifications enable the prompt to accept multiple selections and apply the filter accordingly in the report.