I think it returns at once when it finds the first occurance. This is what "exists" means :-)

----- Original Message -----
From: Bambang P
To: Ali Gökçen
Sent: Friday, September 16, 2005 4:25 PM
Subject: Re: [firebird-support] Re: Is "EXISTS()" cheap?


On Friday, September 16, 2005, 7:03:41 PM, Ali Gökçen wrote:
> --- In firebird-support@yahoogroups.com, Bambang P <bpranoto@g...>
> wrote:
>> In this stored procedure statement:
>>
>> if (exists(select 1 from HOLIDAYS where ADate>=DSTART and
> AData<=DEND))
>> then begin
>> .....
>> end
>>
>> Question:
>>
>> Does the select statement step through all records which meet the
> condition
>> or does it return immediately after the first occurance of the
> condition?


> Hi,
> it is not free but cheapest, if there is an index on ADate field.

> ... where ADate between DSTART and DEND ..
> isn't more clear?

Sorry, I was wrong in my example. ADate is a variable while DSTART and
DEND is fields. Indexes on DSTART and DEND are available.

I am rephrasing my example with your suggestion:

if (exists(select 1 from HOLIDAYS where where :ADate between DSTART
and DEND)) then begin
....

The question remains:

Does the select statement step through all records which meet the
condition?

or

Does it return immediately after the first occurance of the
condition?

Thanks anyway.

--
Bambang P.


I want to move to Theory...Everything works in Theory




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