A FROM clause may be used as the datasource for a data block. A FROM clause is a feature of the Oracle Database Server that allows you to nest a SELECT statement in the FROM clause of a SELECT statement. A FROM clause is a valid query block datasource, but it is not a valid DML block datasource. The value returned from a FROM clause is a subset of records from the original query.
FROM clauses are used to perform joins, lookups, and calculations without having to create a view on the server. FROM clauses can also be used to prototype views and to increase performance.
Using a FROM clause as a block datasource is similar to using an updateable join-view as a block datasource. However, a FROM clause provides more control, because the presence of a DBA is not required to define the view. You should note that the FROM clause produces results that are identical to an updateable join-view from the client side, but that there is no defined view on the server.
Array processing is supported to increase performance by reducing network traffic. Set the Query Array Size property to enable array processing.
Query Data Source Type property
Guidelines for choosing block datasources
Using tables as block datasources
Using transactional triggers as block datasources