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
S" To: Multiple recipients of list ORACLE-L
<[EMAIL PROTECTED]>
<wendy.hopper@ cc:
eds.com> Subject: Query tuning with tablename
alias
Sent by:
[EMAIL PROTECTED]
om
21/11/2002
05:13
Please respond
to ORACLE-L
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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