Relation Aggregator

The Relation Aggregator operator takes as input the output of a relation, treats that output as if it were a database table, and performs a SQL SELECT on that table. The Relation Aggregator operator issues output in the form of a relation.

Use the Relation Aggregator operator when you want to perform SQL operations on a relation.

To Create a Relation Aggregator Operator

1. Drag a Relation Aggregator operator from the Palette to the Design view.

2. Double-click the Relation Aggregator operator.

   The property editor opens with the default name of the Relation Aggregator operator and the output schema name populated. The Property Window displays the schema of the data that is input to the Relation Aggregator operator.

3. In the Select field, specify attributes from which to select.

   Any attribute that you specify must appear in the group-by clause. Attributes that you select as expression entries must be in the form of an attribute name, a literal, or an aggregate function supported by the database you use. Examples include COUNT, MAX, MIN, and AVG.

4. In the Expression field, provide an SQL expression to further delimit your Select statement.

   To save some typing, you can drag input attribute field names from the Inputs area into the Expression field.

5. Optionally specify a Where statement in the Where field to provide a search condition, which cannot have a subquery.

6. In the group by field, specify a comma-separated list of attribute names, indicating how you want to group the attributes in the relation that is output from this operator.

7. Click OK.