Question
Morgan Stanley
IN
Last activity: 12 Oct 2019 12:34 EDT
What is the difference between using Sub report and Class join in report definition
Hi
Both the class join and subreport option are similar, just that we can reuse a report elsewhere when we use a subreport instead of using class directly.
Apart from this do we have any other differences in these options?
I mean when we have a subreport why do we have a class join.
Pegasystems Inc.
US
If it so happens that a Subreport can produce the same result set as a class join, you should use the class join approach since class join is simpler and more direct for the database to perform.
The various types of subselects, (Where, From, Select) are mentioned here: https://www.techonthenet.com/oracle/subqueries.php
A Subreport can generate two types of Where clause subqueries:
- IN or NOT IN clause (Do Not Join Rows)
- Correlated subquery (One or more columns joined to the parent RD)
The closest an RD can come to (1) above is comparing a column to a ValueList or CSV text in the Where clause. This can potentially generate a large amount of ((A = B) OR (A - C) OR...) SQL text. That approach should only be used when it is known the ValueList or CSV test is small.
Accenture Australia
AU
"If it so happens that a Subreport can produce the same result set as a class join, you should use the class join approach since class join is simpler and more direct for the database to perform."
I have the same question in relation to performance. Thank you for clearing this up @pedel. It does make more sense that Join will perform better.