RE: Count(*) not doing a FTS??
- From: "Powell, Mark D" <mark.powell@xxxxxxx>
- To: "'oracle-l@xxxxxxxxxxxxx'" <oracle-l@xxxxxxxxxxxxx>
- Date: Thu, 2 Sep 2004 16:31:05 -0400
I do not believe that Oracle even keeps the rows counts for a table in the
header. This would require updating the information for every insert and
delete which seems to be unnecessary overhead to me.
Reference the following link
http://www.jlcomp.demon.co.uk/faq/count_rows.html for the article "Is there
a good way of counting the number of rows in a table ?" that has explain
plans for numerous count situations: PK exists, no PK, is null, etc...
Using 9.2.0.4
2 -- Insert sql after this line. WARNING - Do not end sql in ';'
3 select count(*) from item_master
4 /
Explained.
ddc1 > set echo off
QUERY_PLAN
----------------------------------------------------------------------
COST CARDINALITY
---------- -----------
SELECT STATEMENT
97 1
2.1 SORT AGGREGATE
1
3.1 INDEX FAST FULL SCAN ITEM_MASTER_PRIME UNIQUE
97 425471
-- Mark D Powell --
-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx]On Behalf Of rjamya
Sent: Thursday, September 02, 2004 11:21 AM
To: Oracle Discussion List
Subject: Count(*) not doing a FTS??
I am sitting in a class and instructor told us that count(*) reads
rowcount from segment header in some (or most?) cases rather than
doign the good ol' FTS. He can't remember exact details, so this email
....
is it true? Which version was this introduced? Someone has a
reproducible test case?
Thanks in advance
Raj
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