Select the join type from the Type list, or keep the default value. Set the Cardinality for each side of the join, or keep the default values. Enter an expression for the join, or click the Expression Builder button to define Click OK to save your work.

8-10 Metadata Repository Builders Guide for Oracle Business Intelligence Enterprise Edition This option is useful for optimizing the manner in which the Oracle BI Server processes multi-database inner joins when one table is very small and the other table is very large. Do not select a driving table unless multi-database joins are going to occur. See Specifying a Driving Table for more information about driving tables.

12. Select the join type from the Type list, or keep the default value.

13. Set the Cardinality for each side of the join, or keep the default values.

14. Enter an expression for the join, or click the Expression Builder button to define

the expression in Expression Builder.

15. Click OK to save your work.

Specifying a Driving Table You can specify a driving table for logical joins from the Logical Joins window. Driving tables are useful for optimizing the manner in which the Oracle BI Server processes cross-database joins when one table is very small and the other table is very large. Specifying driving tables leads to query optimization only when the number of rows being selected from the driving table is much smaller than the number of rows in the table to which it is being joined. When you specify a driving table, the Oracle BI Server uses it if the query plan determines that its use will optimize query processing. The small table the driving table is scanned, and parameterized queries are issued to the large table to select matching rows. The other tables, including other driving tables, are then joined together. In general, driving tables can be used with inner joins, and for outer joins when the driving table is the left table for a left outer join, or the right table for a right outer join. Driving tables are not used for full outer joins. See Defining Logical Joins for instructions on specifying a driving table. There are two entries in the database features table that control and tune driving table performance. ■ MAX_PARAMETERS_PER_DRIVE_JOIN Caution: Use extreme caution in deciding whether to specify a driving table. Driving tables are used for query optimization only under rare circumstances and when the driving table is extremely small, that is, less than 1000 rows. Choosing a driving table incorrectly can lead to severe performance degradation. Caution: To avoid problems, only specify driving tables when the driving table is extremely small - less than 1000 rows. Caution: If large numbers of rows are being selected from the driving table, specifying a driving table could lead to significant performance degradation or, if the MAX_QUERIES_PER_DRIVE_JOIN limit is exceeded, the query terminates. Working with Logical Tables, Joins, and Columns 8-11 This is a performance tuning parameter. In general, the larger its value, the fewer parameterized queries need to be generated. Values that are too large can result in parameterized queries that fail due to back-end database limitations. Setting the value to 0 zero turns off drive table joins. ■ MAX_QUERIES_PER_DRIVE_JOIN This is used to prevent runaway drive table joins. If the number of parameterized queries exceeds its value, the query is terminated and an error message is returned to the user. Identifying Physical Tables That Map to Logical Objects The Physical Diagram shows the physical tables that map to the selected logical object and the physical joins between each table. One of the joins options, Objects and Direct Joins within Business Model, is unique to the logical layer. It creates a physical diagram of the tables that meet both of the following conditions: ■ Tables in the selected objects and tables that join directly ■ Tables that are mapped exist in logical table sources in the business model in the business model To open the Physical Diagram for a logical object: 1. In the Business Model and Mapping layer of the Administration Tool, right-click a business model, logical table, or logical table source.

2. Select Physical Diagram and then one of the joins options.