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

[hoeft]

Thank your for your answer. 

But: Your are wrong, it is possible to enforce the join order in SQL. Dan Tow describes it in his book and I think his book wouldn't have got such a good resonance if he hadn't known what he was writting about.

Consider the following Sql-Statement:
  
  |    select *
  |    from Table1 T1, Table2 T2, Table3 T3
  |    where T1.Key2_ID=T2.Key2_ID
  |       and T1.Key3_ID = T3.Key3_ID;   
  | 

If I want to enforce the join oder T1,T3,T2 this can be easily done:
  
  |    select *
  |    from Table1 T1, Table2 T2, Table3 T3
  |    where T1.Key3_ID = T3.Key3_ID 
  |       and T1.Key2_ID + 0 * T3.Key3_ID =T2.Key2_ID;      
  | 

So it is possible in SQL to enforce the join order I want.

Hoeft

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