An aggregation is a data provider which represents a database column that is aggregated over a set of records. At design-time aggregations have the following properties:
At runtime, aggregations are computed in the context of a foundset. The value is derived from a SQL query, which takes the form of a SQL Aggregate Function and appends the WHERE clause used by the foundset's query.
Assume an aggregation, record_count, declared on the customer table. The aggregation type is count and the column is customerid. The aggregation is available for any foundset based on the customers table.
After the find, the aggregation is re-queried using the foundset's new WHERE clause.
Because aggregations are derived from SQL queries, they may not reflect data changes, seen in the client, but not yet committed to the database. Aggregations will refresh after outstanding changes are committed.
SQL Aggregate Functions may be expensive operations, depending on the size and structure of a database table and the nature of the aggregation. Developers are encouraged to use discretion when working with aggregations. For example, when an aggregation is shown in a table-view form, it may result in a query for each record in displayed on the form, and performance may degrade.