[jboss-user] [EJB 3.0] - HQL/ JPA-QL Query Tuning: How to enforce the join order

[hoeft]

Hi!

I have read the book "SQL Tuning" by Dan Tow and want to optimise the important HQL/JPA-QL queries of my application, but I not sure how to enforce the optimal execution plan :-(.

Consider the following JPA-QL-Query:

  | select o
  | from Operation o
  | where o.order.flight.etd = :flight
  | 

The resulting SQL-Statement:

  | select
  |   ....
  |  from
  |   Operation operation0_,
  |   OrderTab order1_,
  |   Flight flight2_ 
  |  where
  |   order1_.flight_id=flight2_.id 
  |   and operation0_.order_id=order1_.id 
  |   and flight2_.etd=?
  |   

Let's say I want to get the following join order:  Flight, OrderTab, Operation. How can I get it? Exists there a way to enforce this join order with Jpa-QL or HQL? 
If it were possible to enforce the join order with JPA-QL I would only have to change the JPA-QL query, the other application code would remain unchanged:

  | Query query = em.createQuery(<JPA-QL Query which enforces the join order>);
  | Operation op = (Operation)em.getSingleResult(); 
  | ....
  | 

But if the only way to enforce the join order is to execute a sql query instead the HQL-Query, I think would have to write the following code:

  | Query query = em.createNativeQuery(<SQL Query which enforces the join order>);
  | Object[] ar = (Object[])em.getSingleResult(); /*the result of the query won't be an object with the type Operation but an array of objects (the attribute values)*/
  | Operation op = (Operation)new Operation().setAttr1(ar[0]).setAttr2(ar[1]) ...;
  | 

The code above is very clumsy and not very convenient. If sql is the only way to enforce the wanted execution plan, can I let hibernate transform the result of the query into an Operation-object?
The code changes in this case would be minimal:

  | Query query = em.createNativeQuery(<SQL Query which enforces the join order>);
  | Operation op = (Operation)em.getSingleResult();
  | 

Thanks
Hoeft

View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4042797#4042797

Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&p=4042797