Metadata Issues
Follow the suggestions in these topics to help resolve common issues with Pentaho Metadata including the Metadata Editor and the Pentaho User Console components which auto-generate metadata models:
- Managing Multiple Outer-Joins
- Slow Responses or Inconsistent Results in Reports
- Metadata-Based Reports Generated in Version 4.8 Produce Different Results in Version 5.x
Non-metadata related reporting issues are addressed in Report Designer and Reporting Engine Issues. See Pentaho Troubleshooting articles for additional topics.
Managing Multiple Outer-Joins
When you have three or more tables that require outer joins, the order in which the tables are joined is critical. Consider the example below:
In the sample preview below, the entries, 1, 2 ,3, and 4 listed under in TABLE4 are taken and outer-joined with the records in the two other tables. The three other tables contain fewer records. The relationships are defined, but now the order of execution is critical. Relationship A is executed first, followed by B, and then C.
Below is the query that is generated:
The nested join syntax that is generated forces the order of execution:
- Join TABLE1 and TABLE2 (shown in red)
- Join TABLE3 and A = B (shown in blue)
- Join TABLE4 with B = Result
Other orders of execution are just as valid depending on the business context to which they are applied. Another order of execution will generate a different result. To allow business model designers to ensure that user selections are executed in a specific way, a Join Order Key is added to the Relationship Properties dialog box.
The join order key is relevant only in instances in which outer joins are deployed in business models. To make the importance of the execution order apparent, this information is displayed in the graphical view of the model.
It is not mandatory to use uppercase letters, (A, B, C, as shown in the first image), to set the order in which tables are executed. Any alphanumeric characters (0-9, A-Z) can be used. The system will calculate the ASCII values of each character; the values are then used to determine the order of execution. In the example, A, B, C, AA, AB, Pentaho Metadata Editor will execute the table relationships in the following order: A, AA, AB, B, C.
To force conditions that would ordinarily be processed in the JOIN condition to be processed in the WHERE clause, follow the directions below to create a delay_outer_join_conditions custom property.
- Right-click on a business model and select Edit.
- Add a property by clicking the green + icon.
- Select Add a Custom Property and set its ID to delay_outer_join_conditions and select boolean for the Type, then click OK.
- Select the newly-created delay_outer_join_conditions property, then click the checkbox for delay_outer_join_conditions under the Custom heading on the right side of the window, then click OK.
Instead of the conditions being rolled into the JOIN clause, they will be allowed to roll down into the WHERE clause.
Slow Responses or Inconsistent Results in Reports
Your reports may produce slow responses or generate inconsistent results. If a report contains inconsistent or incorrect results, and the SQL command contains several joins, make sure the join order has been specified for that report.
Beginning in version 5.0, inner joins are resolved before outer joins. If you have several tables that require outer joins, the order in which the tables are joined is critical because different join orders produce different results. To make the join order consistent, set the Join Order Key field in the Relationship Properties window. For more information, see Managing Outer Joins.
Metadata-Based Reports Generated in Version 4.8 Produce Different Results in Version 5.x
In version 5.0 of the software, inner joins are resolved before outer joins by default. If you are migrating a report from version 4.8 to 5.x, you can specify which method to use by setting the legacy_join_order parameter in the report’s .xmi file. Set legacy_join_order to true to use the 4.8 method. Set legacy_join_order to false to use the 5.0 method.
In addition to setting the legacy_join_order parameter, set the Join Order Key field in the Relationship Properties window.