Re: ROWNUM. can anybody clarify this to me.
Date: 1995/09/07
Message-ID: <42mehh$16qk_at_news-s01.ny.us.ibm.net>#1/1
In message <42ki05$t7l_at_cardinal.fs.com> - skannan_at_cardinal.fs.com ( S. Kannan) writes:
:> I think you are right. There has been a change in O7.1 in the EXPLAIN PLAN
:> statement. There is now an option called STOPKEY to the COUNT operation.
:> It is documented that the STOPKEY option is a count operation where the
:> number of rows returned is limited by the ROWNUM expression in the WHERE
:> clause. It, however, does not mention if a full table scan is avoided or
:> not. But I timed a query containing a ROWNUM in the WHERE clause and found
:> it to be significantly lesser to infer your conclusion. Thanks for pointing
:> this to me.
It probably depends on the statement. A simple:
select * from table where rownum <= 10;
probably would not scan the whole table. On the other hand:
select *
from table
where rownum <= 10
order by SomeField;
+--------------------------- | Simon Thompson
| Christchurch
| New Zealand Received on Thu Sep 07 1995 - 00:00:00 CEST