The No Rows Extracted in Stage 2 Notice Form

This form appears when the Set Extractor has completed the processing of a set of extraction rules and provides a notice that the Table-To-Table rules did not extract any referentially correct data. In order to understand why this notice is generated, it is necessary to understand how the extraction set stages function in an extraction set. The following discussion is clipped from the extraction set overview help file. If you are unfamiliar with the operation of extraction sets, it might be a good idea to review that document.

Extraction Set Stages

The execution of an extraction set proceeds in three distinct stages. Each stage contains specific types of rule and the stage to which the rule belongs is listed beside the other rule information on the Extraction Rules tab of the Set Designer and Set Extractor. All rules within any one executing extraction set stage must complete before the next stage will begin. Rules from different stages will never execute simultaneously.

An Example of Extraction Rule Stages

Stage 1

Extraction set stage 1 contains Command rules, Where Clause rules and All Rows rules. The Where Clause and All Rows rules provide the base driver data for the extraction set. These rules execute only once, and once complete are never re-activated during that run of the extraction set. Command rules in stage 1 exist to provide a user configurable setup mechanism. For example, they could create temporary tables and perform any pre-execution maintenance tasks that are required.

Stage 2

Extraction set stage 2 contains only Table-To-Table rules, Table-To-Table rules enforce a data relationship between two tables. Essentially, this type of rule examines the rows that have been extracted for a source table and then gets all of the rows required from a target table referentially required to support those source rows. Table-To-Table rules will repeatedly activate in order to ensure that all of the required rows are extracted. Any duplicate rows extracted are automatically sifted out. Once stage 2 of the an executing extraction set is complete, a referentially correct set of ROWIDs will have been stored in the temporary tables in the source schema.

Stage 3

Extraction set stage 3 contains only Command rules. These command rules provide a way to perform user specified post-extract and clean up actions.

How is the No Rows Extracted in Stage 2 Notice Generated?

1. The extraction set has no Where Clause or All Rows rules which provide it with initial driver data. The Table-To-Table rules in stage two will only extract the rows from a target table required to support the rows already extracted from a source table. No rows in the source table means no rows are required in the target table. Zero rows in every table is actually a referentially correct subset. However, zero rows in each table is not terribly useful, so this notice is generated to provide advice. If the lack of driver rows is the cause, then the solution is to provide driver rows - usually this is done by implementing a Where Clause rule.

2. The extraction set has Where Clause or All Rows Rules but no Table-To-Table rules are activated. This means that the table for which rows were extracted by the Where Clause rule is not involved in any table to table relationships as a source. This can easily be confirmed by using the Who-Loads-What tool located on the Rule Tools tab of Set Designer application. Start the Who-Loads-What tool, select the table which is the target of the Where Clause rule in the center panel. If no other tables are listed in the right hand panel, there are no outgoing table to table relationships. The solution in this case is to either choose a different driver table or manually add a Table-To-Table rule which uses the target table of the Where Clause as a source in the relationship.

3. The extraction set has Where Clause or All Rows Rules and some Table-To-Table rules have activated but have extracted no data. This means that the rows which were extracted by the Where Clause rule have no relationship to the rows in the table configured as a target in the Table-To-Table relationships. The solution in this case is to check the join condition on the Table-To-Table rules in which the target table of the Where Clause is used as a source.

The DataBee support team is always happy to provide assistance. If you should need advice on this topic please contact DataBee support at the following address Support@DataBee.com.