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Home -> Community -> Mailing Lists -> Oracle-L -> RE: will the Return Order of rows change with time ?
I understand what you are saying. Most people responded that there is no
guarantee because that is the true answer. In a sense you are correct - if
nothing changes the optimisers approach then in all likelyhood the rows
will come back in the same order each time...
However you are inserting rows into the table, so there is a good chance that the optimiser may "change it's mind" at some point in time. Also, most of our comments have been about returning the rows in the same sequence each time... Promising that this sequence will also match the order in which they are inserted becomes even more difficult. Even today the query may be using an index (depending on the where clause) which may result in a traversal of your table that does not match the insertion order.
For example, if you had an index on "delivery_date" and your query was "select * where delivery_date > sysdate" then the result set will most likely appear sorted by delivery_date, since the index is sorted. Delivery_date may have nothing to do with the order of inserting rows into your table however, since different products may have different delivery schedules.
Therefore what your are asking for is really quite unpredictable. Indeed, I have seen cases where index hints are used to return rows in a specific order without using an order by clause, and these rows definitely don't match their insertion order. Using a hint to force the order of a result set makes me cringe - although it does perform very fast, and can be combined with "where rownum < 100" to return the earliest 100 rows without even reading more than 100 rows from the table - a cute trick.
hth,
Mark.
"Ratnesh Kumar
Singh" To: Multiple recipients of list ORACLE-L <ORACLE-L_at_fatcity.com>
<ratnesh.singh@ cc:
patni.com> Subject: RE: will the Return Order of rows change with time ?
Sent by:
root_at_fatcity.co
m
23/10/2002
16:58
Please respond
to ORACLE-L
Thanks a lot to all those people who replied to my query. answering stephane question : the table is 500MB+ , and there is no unique key since it is a child table. Moreover presently i cannot modify the table.
The general concensus is that there is no guarantee of return
order of rows without using order by clause.
Anybody knows why this is so ?
Oracle must be having a fixed algorith for data access , probably
using the extent map.
Assuming
1. no query parallelism & no deletes/updates to table
2. no index/optimizer/structure changes
the data retrieval path should not change with time for the same query ??
thanks & regards
ratnesh singh
-----Original Message-----
Kumar Singh
Sent: Tuesday, October 22, 2002 4:09 PM
To: Multiple recipients of list ORACLE-L
Hi
I have a very large DW table in which there are only inserts and NO updates/deletes.The table grows by around 2-5 % every week due to new inserts.
I need to return the rows for each customer in the same order as inserted
to
table.Due to design/delivery constraints , i cannot modify the table.
ques 1 : if i do a 'select * from table' with where clause but no order by clause,will the Order of rows returned be the same whenever this query is executed ? Is this guaranteed by Oracle ?
ques 2 : if i export/import this table , then execute the same query, will the Order of rows returned be the same as before the export/import ?
ques 3 : if i use the 'move' cmd to rebuild this table , then execute my query,will the Order of rows returned be the same as before the rebuild ?
any explanations are most welcome....
many thanks
ratnesh singh
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