Re: Query tuning with tablename alias

Wendy,

I have never heard of alias' providing either a performance gain or reduction. One thing I haven't verified though is the impact on hints. It has been my observation that if a table has an alias then that alias must be used in the hint. For example:

select /*+ index(user) */ *
from ctcs_user u;

Does not use an index, whereas:

select /*+ index(u) */ *
from ctcs_user u;

Does use an index.

If you queries are joining tables across instances, however, then I'd be looking there for performance issues. Oracle doesn't join across instances really - it tends to just temporarily copy one table to a different instance. (Someone technical can explain this properly).

Regards,

     Mark.

                                                                                                                   
                    "Hopper, Wendy                                                                                 
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                    21/11/2002                                                                                     
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Hello list.

I have recently been tasked with trying to optimize some slow performing queries (Oracle 8.1.7) for an application that generates reports in a data warehouse type environment. I have noticed in most of the queries that the table names have been aliased, but not used elsewhere in the query.

IE. SELECT table1.column1,

                      table1.column2,
                      table2.column1
       FROM     table1 A,
                      table2 B
       WHERE   table1.key = table2.key;

Are there any advantage/disadvantages to giving these tables aliases and not using them anywhere else? I am thinking that if the tables have been assigned alias names, they should be referred to by alias names, but I guess I have not seen anything documented on this officially. These queries join tables against remote tables in a different instance, if that makes a difference. Any insight on this would be great.

Thanks.

Wendy Hopper

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