Is a crossover query equivalent to a where a and b?

Question

I have a DB with postgresql and I wrote two simple queries

select page from title where word = 'france' and part = 'headline'; 

and

 select page from title where word = 'france' intersect select page from title where part = 'headline'; 

I think that they should return the same result, but actually it is different. Any suggestions?

The table structure is just id, word, page, part.

EDIT:

I also tried

select separate

but a query with intersect always returns some irrelevant results. This is a DB of a simple reverse table of some news web pages. Thus, the page, word, and part are not unique. But there are no duplicate entries.

Answer 1

WHERE (a) AND (b) is the Boolean condition applied to each record. A record is included only if it satisfies all conditions. In other words, only entries in which the word is 'france' AND part are the “heading” will be included at the same time.

What you need is more like using OR in your state?

 select page from title where word = 'france' or part = 'headline'; 

Or are you having problems with multiple posts that link to the same page?

For instance...

 1 | 'france' | 'aaa' | 'headline' 2 | 'france' | 'bbb' | 'body' 3 | 'germany' | 'bbb' | 'headline' 

'aaa' will be returned by your requests.

'bbb' will only be returned by your second request.

Answer 2

The only technical difference that I see is that the crossing operation would create a unique page s. The first can generate duplicates.

Update: They are not the same. the correct answer is what Dems has already explained (I voted for his answer):

 page word part 1 france headline 2 uk headline 2 france body 

word = france AND part = headline => page 1

word = france => page 1, 2 part = headline => page 1, 2

intersection of the previous two sets => p. 1, 2

Update2: The answer to the question: how to make intersect give the same result? The intersection should be performed on the column under conditions like here.

 select page, word, part from title where word = 'france' intersect select page, word, part from title where part = 'headline'