AW: Index use vs Table Scan!

Hello again!

I have real data in the relation and the EXPLAIN-statement states a huge
page count and a table scan, when I use the <= or < operator in the
statement 

        explain select * from s_event where (eventtime < 1111056567313)

and a page count that is much more smaller and the use of an index, when I
use the  statement 

        explain select * from s_event where (eventtime = 1111056567313)

The manual and the section you mentioned doesn't explain this behaviour, at
least I haven't found the explanation.

Any further hints/tipps?

Thanx a lot!

Chris

-----Ursprüngliche Nachricht-----
Von: Grossmann, Gert [mailto:gert.grossmann@xxxxxxx]
Gesendet: Freitag, 18. März 2005 09:07
An: maxdb
Betreff: AW: Index use vs Table Scan!


Simple check access path with "EXPLAIN SELECT ... ". Now you can see if
index or key is used. For further information please read manual section
'Background Knowledge/SQL Optimizer'.

Gert

-----Ursprüngliche Nachricht-----
Von: Christoph Weser [mailto:Christoph.Weser@xxxxxxxxx] 
Gesendet: Freitag, 18. März 2005 08:50
An: Grossmann, Gert
Betreff: AW: Index use vs Table Scan!


Hello Gert!

Thanx for your quick replay and a simple answer.....how do I check the
access paths and how to interpret results?
There are right now some real data in the table...a few million rows.

Thanx a lot for your help!

Chris

-----Ursprüngliche Nachricht-----
Von: Grossmann, Gert [mailto:gert.grossmann@xxxxxxx]
Gesendet: Freitag, 18. März 2005 07:02
An: maxdb (E-Mail)
Betreff: AW: Index use vs Table Scan!


MaxDB has a cost based optimizer. Without any data in relations there is no
difference between table scan vs. index access.
Fill your releation "s_event" with real data and then check access pathes.

Gert

-----Ursprüngliche Nachricht-----
Von: Christoph Weser [mailto:Christoph.Weser@xxxxxxxxx] 
Gesendet: Donnerstag, 17. März 2005 17:29
An: maxdb (E-Mail)
Betreff: Index use vs Table Scan!


Hello All!

I'm running 7.4.3.32 on a W2K system.

I have the table: 

create table s_event (
       EID FIXED(38,0) NOT NULL, 
       ETID FIXED(38,0) NOT NULL,
       SID FIXED(38,0) NOT NULL,
       CID FIXED(38,0),
       eventtime FIXED(38,0) NOT NULL,
       data LONG BYTE,

       FOREIGN KEY(ETID) references s_eventtype(ETID)
)

//
create index s_event_x1 on s_event(EID)
//
create index s_event_x2 on s_event(ETID)
//
create index s_event_x3 on s_event(SID)
//
create index s_event_x4 on s_event(CID)
//
create index s_event_x5 on s_event(eventtime)

When I do an 

        explain select * from s_event where (eventtime < 1111056567313)

the result is a table scan!

On the other hand, when I do an 

        explain select * from s_event where (eventtime = 1111056567313)

The DB does an index scan and it uses the index s_event_x5.


Is there a way for the first statement, that the db also does an index scan
and not the expensive table scan???
Why isn't an index also used in the first statement? Any explanations?

Thanx a lot to everyone!!!

Chris

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