Posted by Hugo Kornelis on 08/28/05 22:10

On 27 Aug 2005 08:50:45 -0700, coosa wrote:

>Your logic is quite interesting and i'd like to learn much from you.
>First, select '%'+@search_key1+'%' or select '%'+@search_key2+'%' etc.
>would bring some results, then why do you write "where NOT exists"?

Hi Coosa,

Remember back at school, when your English teacher told you: "Don't use
no double negations, not never"?

He was wrong.

I didn't take the time to go over all details in Steve's post, but at
first glance it lloks just like the "relational division" I mentioned in
my previous post.

You wanted to find items that satisfy all search terms. Steve put the
search terms in a derived table, then went on to use the standard
solution for finding a match that satisfies all rows - by rephrasing it
with a double negation:

"Find items that match all search terms" --> "Find items for which there
is no search term that it doesn't match".

Hence the use of not one but actually _TWO_ not exists conditions.

Best, Hugo
--

(Remove _NO_ and _SPAM_ to get my e-mail address)

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