Re: Re-Reason of Slowness of Query

23.03.11 12:19, Adarsh Sharma написав(ла):

Vitalii Tymchyshyn wrote:

23.03.11 12:10, Adarsh Sharma написав(ла):

I just want to retrieve that id 's from page_content which do not have any entry in clause2 table.

Then
select distinct(p.crawled_page_id) from page_content p
 where NOT EXISTS (select 1 from  clause2 c where c.source_id = p.crawled_page_id);
is correct query.

I can't understand how select 1 from  clause2 c where c.source_id = p.crawled_page_id works too, i get my output .

What is the significance of 1 here.

No significance. You can put anything there. E.g. "*". Simply arbitrary constant. Exists checks if there were any rows, it does not matter which columns are there or what is in this columns.

Best regards, Vitalii Tymchyshyn