Publishing Reports to the Web - Downloads - Oracle

Note: The only meaningful place to use the SRW.SET_MAXROW()
built-in procedure is in the Before_Report trigger (after the query has
been parsed). Calling the SRW.SET_MAXROW() built-in procedure
after this point raises the SRW.MAXROW_UNSET built-in exception.
The query will still be parsed and bound, but no data will be
returned to the report.
Methodology
You can define a query based either on an XML or a Text pluggable data source by
selecting the fields to be used in the query (i.e., all available fields or a subset). If you
must use a subset of the fields, do so at the query level using parameters, as opposed
to fetching all the values and filtering them using a group filter or layout level format
triggers.
20.1.2.5 Break Groups
Limit the number of break groups to improve your report’s performance. Oracle
Reports sets the break level for each column in the data model that has the break order
property set except the lowest child group.
For a SQL query, Oracle Reports appends this as an extra column to the ORDER BY
clause in the query. The fewer columns in the ORDER BY clause, the lesser the work
the database has to do before returning the data in the required order. Creating a break
group may render an ORDER BY clause redundant inspite of defining it as part of the
query. Remove any such ORDER BY clauses as it requires extra processing by the
database.
If your report requires the use of break groups, set the break order property for as few
columns as possible. A break order column is indicated by a small arrow to the left of
the column name in the group in the Reports Builder Data Model view. Each break group
above the lowest child group of a query requires at least one column to have the break
order property set. Removing the break order from columns where sorting is not
required increases performance.
Limit break groups to a single column whenever possible. These columns should be as
small as possible and be database columns (as opposed to summary or formula
columns) wherever feasible. Both conditions help the local caching that Oracle Reports
does, before the data is formatted for maximum efficiency. Clearly, these conditions
cannot always be met but can increase efficiency whenever utilized.
20.1.2.6 Group Filters
Group filters reduces the number of records retrieved from the data source. Filtering
takes place after the query returns the data (from the data source) to Reports Builder.
Even if the filter is defined to display only the top five records, the result set returned
to reports will contain all the records returned by the query. Hence, it is more efficient
to incorporate the group filter functionality into the query’s WHERE clause or into the
maximum rows property, whenever possible. This restricts the data returned by the
database.
20.1.2.7 To Link or not to Link
There are a number of ways to create data models that include more than one table.
Consider the standard case of the dept/emp join, with the requirement to create a
report that lists all the employees in each department in the company. You can create
either of the following:
■ Single query
Tuning Oracle Reports 20-11