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From "Antonio Gallardo" <agalla...@agsoftware.dnsalias.com>
Subject Re: [ESQL] Improvement....
Date Mon, 27 Jan 2003 08:49:08 GMT
Niclas Hedhman dijo:
> On Monday 27 January 2003 16:01, Torsten Curdt wrote:
>> Niclas Hedhman wrote:
>> > On Monday 27 January 2003 07:06, Torsten Curdt wrote:
>> >>>What do the database to try to find the 6th row?
>> >>>
>> >>>I think the answer is: scan the rest of the database after finding
>> the ONLY 5 rows that already exist.
>> >>
>> >>No :) ...be sure - it doesn't
>> >
>> > Well, that depends on the WHERE clause. For instance;
>> >
>> > WHERE SQRT(  SQ( a - b ) + SQ( c - d ) + SQ( e - f ) ) < g ;
>> >
>> > definately go through every record, whether the fields are indexed
>> or not.
>>
>> Aaah - now I got you guys! (sorry for being that slow ;)
>>
>> Antonio, how comes that you always know you have 5 rows? This sounds
>> quite unusual to me...
>
> I can answer part of that;
>
> 1. You have the "count" from somewhere else.
> 2. You know that objects of type X has N attributes, always fixed. 3. I
> have 10,000,000 random records of N types. I want the first one of each
> type.
>
> Sure there are other cases.
>
> Niclas

Thanks Niclas!

This is the example I tried to explain:

I have a table that store the status of some tickets. You always know how
many status there can be. If you said:

1-Open
2-Close
3-Invalid

Then if you want to show the history, you will ask for LIMIT 3, but the
database will try to find the 4th row after finding the only 3 that can
exist.

This is why I told this is a performance issue. Not an error.

Antonio Gallardo
>
>
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